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Retro-fitting supplementary gauges

Discussion in ''How To' & 'Handy Hints'' started by Nigel, Jan 25, 2009.

  1. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Eyes Down For Data

    Sometime during the late-1970s or 1980s, the following article, which briefly outlines the importance of instrumentation and the benefits of retro-fitting supplementary gauges, appeared in an issue of Drive, a magazine which was published regularly by the Automobile Association and provided free to members.




  2. kommodius

    kommodius Active Member

    Nice one Nigel.

    Poor old Sister Standish!

    Ray & da Boyz
  3. jon ward

    jon ward Active Member

    Travelling Australia

    13 pounds for a head gasket! :eek: I wanna go to that mechanic!:lol:
  4. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    I recently discovered that I had transcribed & edited the above article, incorporating comments, relevant to VWs with air-cooled engines.

    Sometime during the 1970s, the following article, which briefly outlines the importance of instumentation and the benefits of retro-fitting some common supplementary gauges, appeared in an issue of Drive, a magazine which was published regularly by the Automobile Association and provided free to members.

    Readers wishing to gain a more detailed insight into this topic, are advised to read my comprehensive article, entitled, "Air-cooled Volkswagens: The Case For Supplementary Instrumentation", which examines the rationale for retro-fitting various supplementary gauges, warning lights, buzzers and other instruments; some of which are regarded as essential, whilst others are merely desirable, under specific circumstances. Most are associated with engine operating conditions and of its ancillary equipment, but some relate to vehicle operation, navigation and safety. The article does not describe how to fit the instrumentation, but merely examines the reasons for doing so, in a broad context.



    Transcribed & Edited by Nigel A. Skeet

    When researchers from the AA's Drive magazine, logged the misfortunes of 6,000 motorists, stranded by Britain's motorways, during one August holiday fortnight, sometime in the 1970s, they discovered that nearly 2,000 had suffered cooling and oil system damage.

    Of 213 drivers replying to a follow-up questionnaire, on the costs of their breakdown, 75 had misinterpreted, failed to recognise or ignored information from their instruments or warning lights. The cost to these owners, was more than £4,000 in repair bills and hire car charges. To rub in the salt, the repairs took a total of 491 days to do.

    Sister Standish, a nun travelling to Heathrow along the M4, had a burst radiator hose and blew the head gasket of her convent's Mini. "The temperature was rising on the gauge, but I hoped the car would last until I reached the airport", she said, when the AA towed her to the nearest garage. Sister Standish's penalty for ignoring the warning was a bill of over £13 and a week's delay while the car was repaired.

    Instruments and warning lights are a continuous monitor of the car's health and if correctly interpreted, signal when servicing and repair, might avoid more expensive damage.

    The only instrument that by law, a car must have, is a speedometer. This isn't necessarily very accurate, as the law permits a 10% error; a reading of between 63 MPH and 77 MPH, at a true speed of 70 MPH. In fact, most speedometers err on the high side, which has the advantage of keeping drivers within speed limits. Additional information may be available on the speedometer, in the form of coloured dots or stripes, which indicate the maximum advisible speed, in each of the car's lower gears; in simple language the speeds at which gear changes should be made, to avoid engine damage.

    This is an important job performed by a rev-counter, otherwise known as a tachometer, which is found on the more expensive cars and sports cars, but which may also be added as an auxiliary instrument. The rev-counter needle should rarely be allowed to move onto the orange and red segments or lines on the dial; these regions indicating the engine speeds which increase wear or cause damage.

    Basic cars in a model range, may have only one other dial; this normally being a fuel gauge (some early air-cooled VWs, didn't even have this). On a new car, it is advisible to run the tank dry; keeping a reserve gallon of fuel in reserve, to check how far the car will go with the gauge showing empty. Warning lights usually provide the rest of the car'semergency data.

    The ignition light, wired direct to the control box (i.e. voltage regulator), the heart of the car's electrical system, displays one piece of information. When the light is on, it means that the battery is supplying the car's electrical power. When it is off, the generator is helping to meet current demands. The light should go out or flicker, when the engine idles. If the ignition light comes on when the car is running, stop as quickly and as safely as possible. A common reason is a broken fan belt – to drive on would overheat the engine (not applicable to the VW 411 & 412, VW Porsche 914-4, 1972~83 VW 17/18/2000 Type 2 and 1980~83 VW 1600 Type 2).

    If the fan belt is intact and at the correct tension, the fault probably lies in the generator (i.e. alternator or dynamo) or in the control box (i.e. voltage regulator). The car can be driven to the nearest garage quite safely, because the battery will continue to power electrical components. However, you stand more chance of getting there, if all accessories like the heater and the heated rear window are switched off.
    Last edited: Jul 9, 2011
  5. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retrofitting supplementary gauges


    Transcribed & Edited by Nigel A. Skeet

    The ammeter is a useful supplement to the ignition warning light. It shows when the battery is being charged or discharged (provided it is correctly incorporated into the battery charging circuit) and measures the amount of current involved. When the car's engine is started, the ammeter's needle will climb up the positive side of the scale, to show a reading of about 10 amps. The car's control box (i.e. voltage regulator) soon reduces the charge and the needle then swings back to near zero – the sign of normal running.

    A negative or discharge reading on the ammeter is quite correct if the engine has stopped, but accessories like the lights or wipers are still on. A discharge reading while the engine is running, however, may mean that the generator can't cope with the car's current demands (switch off some accessories) or that the fan belt is loose or glazed. The ammeter usually gives a steady reading. If the needle flickers a lot, there may be a fault like a loose connection. Switching each item of the car's equipment on separately, may betray the faulty circuit.

    Some manufacturers fit a voltmeter (sometimes called a 'battery condition indicator'), an instrument with a slow-moving pointer (not true for all voltmeters; especially VDO Cockpit voltmeters) that registers the reaction of the battery to electrical loads placed on it. A good battery, with clean, well-made connections, will give a voltmeter reading of about 12V when the ignition is switched on and the engine is static. A lower reading reveals that the battery's useful life may be almost be over.

    The reading should be higher with the engine running – about 13·5V, the generator's charging voltage. A lower or higher voltage, probably means the control box (i.e. voltage regulator) needs attention. The ammeter and voltmeter are useful instruments to fit, if the car has no standard electrical gauges.

    Fan belt breakage will bring on the ignition warning light, but it will also be given away by a rapid upward swing of the needle on the water temperature gauge (cylinder-head-temperature gauge, in the case of most VW air-cooled engines; assuming one is fitted). The normal running temperature of a water-cooled car's cooling system, is between 85ºC and 95ºC. The hotter the engine runs, the more efficient it becomes; but there is a danger limit – about 110ºC – which is set by the system's operating pressure and the boiling point of the water and anti-freeze coolant mixture.

    A gauge gives a fuller interpretation of the car's ills than a warning light. Persistent low temperatures show a thermostat fault (it is probably stuck open), while a continuous temperature rise from cold starting to overheating, can signal a closed thermostat. Never continue driving with a temperature warning light on, or when the gauge shows a sudden temperature rise – these are the symptoms of hose leaks, radiator blockages or cracked cylinder-head gaskets.

    The oil-pressure warning light and oil-pressure gauge, can indicate more serious engine failings. The glittering of the oil warning light while driving, demands an immediate stop to search for oil leaks (especially around the oil filter – sadly lacking from most VW 12/13/15/1600 Type 1, 2 & 3 air-cooled engines!), a check on the car's oil level or evidence of oily smoke. Don't drive on, even slowly, with the oil light showing – expensive big end bearing damage may result.

    The oil-pressure gauge can provide an earlier warning of trouble. When the engine is idling, the oil pressure should be 20~25 PSI (not this high for an air-cooled VW air-cooled engine, whose clearances are larger than for water-cooled engines). On the road, the pressure stabilises at 45~55 PSI, when the oil has warmed up. A reading more than 10 PSI lower than the car's normal oil pressure, should be thoroughly investigated.

    An attractive, functional addition to the car's fascia, is a vacuum or performance gauge. Skilled reading of this instrument, which records the continuously changing pressure inside the inlet manifold, under various conditions of engine load, can point to hidden faults like manifold leaks, a choked air cleaner or piston ring wear. Watching the gauge carefully and keeping the needle at the high vacuum end of the scale, can make for better petrol economy.

    Warning lights could be more effective, if manufacturers standardised the signal colours. Main beam lights are almost always blue; but oil warning lights may be red or green. (red on many air-cooled VWs and green on my Triumph Toledo). As more and more dashboard lights become common on cars, makers must agree an international code of colours, to arrest the driver's attention immediately.

    A word of warning; don't become too dial pre-occupied when driving, for a one-second glance at 60 MPH, will leave the car 'unattended' for a distance of 88 feet. Instead, add a few minutes' instrument inspection to the weekly maintenance schedule and on the move, study the instruments only when the road ahead is clear.
    Last edited: May 9, 2009
  6. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet



    Basic Supplementary Instrumentation

    Oil Pressure

    Oil Level

    Oil Temperature

    Cylinder-Head Temperature

    Engine Inlet, Combustion-Air Temperature

    Exhaust Gas Temperature

    Inlet Manifold Vacuum Pressure

    Turbocharger or Supercharger Boost Pressure

    Engine Speed

    Air / Fuel Ratio & Excess Air Factor Lamda

    Detonation, Knock or Pinking


    Ambient Atmospheric Pressure or Altitude (i.e. Height Above Sea Level)

    Battery Charging & Electrical Supply

    Ambient-Air Temperature & Frost

    Time of Day

    Fuel Level

    Vehicle Service Intervals

    Direction Indicators

    Pitch & Roll Angles

    Satellite Navigation

    Brake Circuit Failure

    Brake Light Operation

    Tyre Pressures

    Accessory Warning Lights

    The Author's Present & Possible Future Instrumentation System

    Electrical & Vacuum Connections

    Instrument Wiring Colours

    Available VDO 'Cockpit' or 'Proficockpit' Gauges

    Available VDO Gauge Senders & Warning Device Switches

    Other Available Gauges, Senders, Switches & Warning Devices

    Gauge Sender Installation Adapters


    Useful Addresses


    Even by modest standards, the stock air-cooled VW, is poorly equipped with instrumentation; having only a fuel gauge (not all model years!) and speedometer, plus warning lights for low oil-pressure, generator (alternator or dynamo) supply voltage, direction indicators, headlamp main beam and parking lights (not all model years); which experience has proven to be wholly inadequate.

    Two notable exceptions, were some of the German military specification, 1968~79 VW Type 2s (see David Eccles & Andreas Plogmaker, "Atten-Shun! Herr Oberst Reporting for Duty", Volkswagen Camper & Commercial, Issue 14, Spring 2004, Pages 22~25) and the post-1984, Brazilian manufactured, VW Super Fusca (i.e. Super Beetle), which were equipped with an oil-temperature gauge and rev counter!


    Most vehicle instrumentation systems, comprise gauges and warning lights; the former of which gives precise information about prevailing conditions, whilst the latter warns if these conditions deviate beyond acceptable limits. According to ergonomics research pertaining to the aeronautical, chemical process and nuclear industries, humans are better at making decisions, once warned of a situation, than they are at continuously monitoring gauge readings. Hence, gauges should be regarded as complementary to warning lights, not as substitutes! However, unless observed at the moment of illumination, conventional warning lights may easily go unnoticed, so ideally these should be linked to a single flashing light or buzzer (VW part No. 111 951 307B – plugs into an accessory relay, mounting cum connector block), which are more likely to attract one's attention.

    In this article, I discuss the desirability and availability of the various supplementary gauges and warning light or buzzer systems, plus outlining some systems, which could usefully be adapted, from other standard production vehicles, using a little lateral thinking and technical knowhow. Where appropriate, I also cite examples from my own experience and that of other owners, where the possession of supplementary instrumentation, has proved to be invaluable or would have been invaluable, had one had it at the time.


    Several months before his untimely death in August 1996, Arthur Barraclough and I, corresponded about our respective 1968~79 VW Type 2 modifications and upgrades, which included the issue of supplementary instrumentation. Arthur and his wife, together with their celebrated 1970/71 VW '1600' Type 2, "Rosie" (equipped in 1982, with a 1976~79 VW 2000 Type 2 engine, following repeated problems with standard and upgraded versions of the VW '1600' Type 2 engine), had travelled 217,000 miles visiting much of the World, including 57 countries, 10 deserts and a few mountain ranges, one of which was the Himalayas, with mountain passes exceeding 13,000 feet in altitude.

    He regarded as "essential instruments", an oil-pressure gauge, oil-temperature gauge, ammeter, rev-counter and altimeter. In his words, "He needed to know what was going on, because if he broke down in the middle of Afghanistan or crossing the Sahara, he couldn't call National Breakdown". Whether one would classify an altimeter as essential, would depend upon the terrain over which one drives, but based upon my own experience, I would also add to his list, a cylinder-head temperature gauge, vacuum gauge and voltmeter, plus a complementary set of warning lights, where practical.

    Arthur Barraclough's much vaunted, modified 1970 VW Type 2


    Oil-pressure and oil-temperature gauges, are factory-fitted instruments, on the air-cooled Porsche 911 and many of the VW-Porsche 914-4 & 914-6 cars; which should be regarded as the absolute minimum complement of supplementary instruments. These, together with a voltmeter, vacuum gauge and rev-counter are easy to fit, requiring minimal disturbance to either the engine or electrical system.When next the engine is removed for maintenance, use the opportunity to fit a cylinder-head temperature gauge, preferably with a sensor on each cylinder head.

    Fitting an ammeter, is not fundamentally difficult, but it does necessitate modification of the charging circuit, if the gauge is to indicate whether the battery is being charged or discharged, rather than merely showing that current is being supplied to the electrical system by the battery and/or generator, without distinguishing between them, as I suspect Arthur Barraclough's did. Good quality gauges, bought new, are not cheap (relatively inexpensive when bought second-hand or as new-old-stock), but neither are replacement engines nor towing & recovery services, especially when touring overseas, as I discoverd in Sweden!
    Last edited: May 30, 2010
  7. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet


    In a brief article entitled, "Eyes Down for Data", from an issue of the AA's Drive magazine, dating from the late-1970s or early-1980s, stated that when the magazine's researchers had logged the misfortunes of 6,000 motorists stranded by Britain's motorways during one August holiday fortnight, they discovered that nearly 2,000 had suffered cooling and oil system damage. Of 213 drivers replying to a follow-up questionnaire, on the costs of their breakdown, 75 had misinterpreted, failed to recognise or ignored, information from their instruments or warning lights. The cost to these owners, over thirty years ago, was more than £4,000 in repair bills and hire car charges. To add insult to injury, the repairs took a total of 491 days to complete!

    The article then went on to review the benefits of fitting an oil-pressure gauge, water-temperature gauge (calibrated in ºC or ºF, rather than merely indicating Cold, Normal & Hot), vacuum gauge, rev-counter, ammeter and voltmeter, as supplementary, accessory instruments. Being aimed primarily at owners of cars with water-cooled engines, the article made reference to a water-temperature gauge, rather than oil & cylinder-head temperature gauges, which are appropriate to air-cooled engines. The rationale behind the article, was that by the sensible use and interpretation of a comprehensive instrumentation system, developing problems could be identified in their infancy, enabling one to avert disaster in extreme cases, but more usually to plan preventative maintenance or repair, which would avoid breakdowns occurring.


    Crucial to the well being of any engine, is the adequate lubrication of all moving parts, for which the maintenance of correct oil pressure is critical. To monitor this, the VW is fitted with an oil-pressure switch, which typically illuminates a warning light, when pressure falls below 0·30 ± 0·15 BAR. For some engines, this may be satisfactory at idling speed, but at higher engine speeds and when under load, the engine requires greater oil pressure, to maintain adequate lubrication.

    In their technical data, Volkswagen specify for their air-cooled engines, that at 2,500 RPM and with an oil temperature of 70°C, the oil pressure of SAE 30 monograde oil, should normally be 3 BAR; subject to a minimum lower limit of 2 BAR. This implies that the oil-pressure warning light may not illuminate until considerable damage has already been incurred; the engine possibly having suffered the effects of gradually diminishing oil pressure, for some time! In the case of excessive oil pressures, the standard warning light system, will never give any warning.

    VDO Cockpit, 0~5 Bar oil-pressure gauge


    In order to monitor the engine's health and give forwarning of uncharacteristic trends (either progressive increases or decreases) in oil pressure, an oil-pressure gauge (ideally of 0~5 BAR range) is a necessity. To alert the driver to sudden oil pressure changes, a warning light or buzzer is required. As already stated, the standard break-on-rise, 0·30 ± 0·15 BAR oil-pressure switch, is of limited value.

    Some of the 1983~92 VW Type 2s, with water-cooled, petrol engines, are equipped with an additional oil-pressure switch, which closes at 0·90 ± 0·15 BAR, whilst certain other VW & Audi water-cooled engines, manufactured since the mid-1980s, have an additional break-on-fall switch (VW Part No. 056 919 081E), which closes at 1·8 ± 0·2 BAR, incorporated into an electronic circuit, whereby a buzzer sounds, if pressure falls below this limit, at engine speeds in excess of 2,000 RPM. Either one or both of these additional switches, would be beneficial for the VW air-cooled engine, but I believe that a system, similar to the latter option would be particularly useful. If available, it would also be desirable, to fit a break-on-fall, oil-pressure switch, which closes at circa 4~5 BAR, to warn of excessive oil pressures.

    I speak of 'uncharacteristic trends' and 'sudden changes', because both increases or decreases in oil pressure, may be symptomatic of oil starvation. These however, should not be confused with the pressure variation which naturally occurs, owing to changes in engine RPM or warming of the oil, to normal operating temperature. My family's 1973 VW 1600 Type 2 engine, running on Mobil 1, SAE 5W/50 fully synthetic oil, typically exhibited oil pressures, of 3·5~4·0 BAR just after starting up from cold (even below 0ºC, during severe British weather conditions!), 3·0 BAR under normal driving conditions and 1·0 BAR at idle.

    Reduced oil pressure may arise for a variety of reasons, which include:- too little oil (owing to oil consumption or leakage) or too much oil (oil whipped up by the camshaft and crankshaft, entrains air, causing the oil to be frothy!) in the crankcase; broken or weakened oil-pressure relief and/or control valve springs; excessive bearing clearances; worn oil pump; oil surge; restriction (or even blockage!) of the oil filtration system; inadequately low viscosity of engine oil; or even severe engine overheating, which radically decreases oil viscosity.

    A slight reduction in oil-pressure, as a result of reduced viscosity, is well documented (see Jim Tyler, "Project Beetle: How Hot?", VW Motoring, October 1997, pages 44~45) as an early sign of engine overheating. However, it is doubtful whether this would give a sufficiently early warning, in cases where there was a sudden loss of the cooling system, as discovered by the Reverend Paul MacCarty (see Transporter Talk, Issue 46, April 2000, pages 39~40), when the oil-pressure warning light illuminated, the instant before his VW 1600 Type 2 engine expired!

    Although relatively rare, cases of excessive oil pressure can and do arise, being attributable to faults, such as:- oil-pressure control and/or relief valves, which have either siezed, or whose springs are of the wrong specification; restriction (or even blockage!) of the oil galleries and/or oil cooler; or excessively high viscosity oil (e.g. viscosity specification inappropriate to the prevailing local weather conditions). High oil pressure can lead to increased oil consumption (more oil mist generated in the crankcase, then enters the combustion chamber via the breather and air filter; increasing the risk of detonation, owing to the effective reduction in fuel octane rating!) and leakage.

    There is also the possibility of a ruptured oil cooler, in extreme cases. I have learned of cases in the USA and Canada, where oil-filter cartridges have ruptured, owing to the increased oil-pressure, resulting from the high viscosity of SAE 30 monograde engine oil, used during the extreme cold, of North American winters. Even "low-viscosity" SAE 10W/40 oil, has the consistency of cold mollasses, at temperatures falling much below –20 ºC; a warm winter's day in parts of Canada and northern Scandinavia.

    Many of the aforementioned problems, may be avoided by regular oil changes, using a good quality oil, of an appropriate viscosity range, cleaning the oil strainer mesh and replacing the full-flow, oil-filter cartridge (a desirable after-market accessory, if not already a standard fitment), at the stated intervals, together with ensuring that the engine oil operates within an acceptable temperature range. Oil starvation, whether through blockage (carbonised oil, 'black sludge' or bearing fragments, etc.) or lack of oil pressure, leads to increased friction, overheating and ultimately engine siezure.

    Rapid oil leakage, is probably the most widely documented (see various readers' letters, in past issues of Transporter Talk and other VW magazines) cause of engine siezure. In many cases, illumination of the oil-pressure warning light, alerted drivers to the existence of the problem, just moments before the engine died, accompanied by a loud bang and/or a cloud of dark coloured smoke! Many years ago, despite regular oil-level checks, I narrowly avoided engine siezure, when the crankcase breather of my 1973 VW 1600 Type 2, twin-port engine, was blocked, resulting in 80% of the 2·5 litres of oil leaking out, owing to crankcase pressurisation (probably exacerbated by worn valve guides!), over a distance of 80 miles.

    Similarly, my first warning of this, was when the oil-pressure warning light (activated by the standard 0·30 ± 0·15 BAR oil-pressure switch), started to flicker on and off, arising from the partial immersion of the oil-pump, pick-up tube, as the remaining quantity of oil, slopped to and fro, in the crankcase (i.e. sump). The oil leak would have been discovered much sooner, had a supplementary oil-pressure switch (with a greater activation pressure; e.g. 0·90 ± 0·15 or 1·8 ± 0·2 BAR) or an oil-pressure gauge, been fitted at the time.
    Last edited: Jul 9, 2011
  8. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet

    OIL PRESSURE continued

    Although unfamiliar to most VW owners, oil surge is a relatively common phenomenon, to which the VW flat-four engine is particularly prone (see Peter Noad, "Pace Notes", VW Motoring, November 1997, pages 40~41); resulting from centrifugal effects, which cause the oil to surge out of the crankcase, through the pushrod tubes and into the valve rocker box covers, under conditions of 'high-speed' cornering. This leads to there being inadequate oil in the crankcase, such that the oil pump pick-up tube is not fully immersed and so sucks up a mixture of oil and air, which does not provide adequate lubrication; yet another reason to ensure that the oil level is always at the maximum mark.

    'High speed', is a relative term and in the case of the flat-four engine, oil surge can occur, even under normal driving conditions, with a VW 1200 Beetle and probably also a VW Type 2, which is a remarkably agile vehicle, when skillfully driven. With the aid of an oil-pressure gauge, one has the option of changing one's driving style in order to avoid oil surge or alternatively, to implement one or more of the recognised engine modifications, to combat it; these being, a supplementary deep sump, a set of 'windage style' pushrod tubes and an oil windage tray (a standard fitment in the VW 411LE engine crankcase, which can be retro-fitted to the 1972~83 VW 17/18/2000 Type 2 engine, as I have done with my 1911cc, VW 17/1800 Type 2 & 4 hybrid engine).


    In order for the oil pump to maintain the required pressure, it must never be starved of lubricating oil, so the oil must be maintained above a certain minimum level. Conversely, if the level is too high, the crankshaft 'big ends' and connecting rods, will dip into the oil, which churns it up, causing it to become aerated. These have the effect of rendering the oil less effective as a lubricant, substantially increasing frictional losses, generating heat and incresing fuel consumption. The traditional dipstick, on which are marked the recommended maximum and minimum levels, is probably still the simplest and most reliable method of determining the engine oil level in the sump.

    Although, on long-distance touring holidays or other long journeys, I have always checked the oil level with the dipstick, on a daily basis (sometimes twice daily, on long, fast stretches!) and weekly at other times, few other motorists are this diligent. Hence, an oil level transducer, coupled to a warning device, would be useful. It has been stated (see T. K. Garrett et al, "The Motor Vehicle", Butterworth-Heinemann, 13th Edition, 2001, page 640) that electronic engine-oil level detection, has been adopted increasingly since the early-1970s.

    The piezo-electric transducer, is normally positioned, to detect when the oil level falls below the minimum mark on the dipstick. It might also be possible to position an additional transducer, to detect when the sump has been overfilled above the maximum dipstick mark, as is all too common in many garage workshops. If an oil level detection system were fitted, it is probable that the driver would be warned of leakage even earlier, than that provided by an oil-pressure gauge or supplementary oil-pressure switch, with higher than standard activation pressure. Similarly, it might also be better suited to detecting oil surge!

    An American-made, after-market, oil-level monitoring device, called the Engine Sentry (see More Products, VW Motoring, September 1999, page 70), which screws into the engine block, is said to use solid-state circuitry, to activate a warning light, if the oil level falls by more than two pints (whether US or Imperial pints, was not stated!). The device is available in Great Britain, from the German Car Company.


    Unlike most cars with water-cooled engines, plus the Porsche 911, 912 & 914, the air-cooled VW was never equipped as standard, with any means of engine temperature monitoring, so the first signs of an overheating engine are:- a noticeable reduction in oil pressure (assuming an accessory oil-pressure gauge or high-pressure switch had been fitted!); noticeable loss of power (assuming one is sensitive to such things!); the acrid smell of burning oil, accompanied possibly by billowing smoke; or loud, 'expensive' noises, as the engine undergoes its final death throes.

    For an air-cooled engine, the oil plays a crucial role, both for lubrication and cooling, so oil temperature, is an important indicator of the engine's running condition. To obtain long-term, reliable operation, it is suggested that once the engine has attained its 'normal' operating temperature, the oil temperature should be maintained between certain upper and lower limits. Opinion differs as to what those limits should be, but the maximum 'safe' oil temperature, for an air-cooled VW engine is generally regarded as being circa 110~120 °C (as measured in the 'sump').

    The magnesium alloy crankcases of the VW 12/13/15/1600 Type 1, 2 & 3 engines, become increasingly elastic, as temperature increases (see Tom Wilson, "How to Rebuild Your Volkswagen Air-Cooled Engine", HP Books, 1987, page 85); quoted as being about 2% and 6% elastic at 105 °C and 115 °C respectively. At the higher temperature, the crankcase easily distorts as a result of crankshaft whip and other unbalanced forces. Consequently, 105 °C should probably be regarded as the upper limit, for dependable longevity of magnesium alloy crankcases.

    Aluminium alloy crankcases, used in what is commonly referred to, as the VW Type 4 engine (found in the 1972~83 VW 17/18/2000 Type 2, VW 411 & 412 and VW-Porsche 914-4, plus some Porsche 912s), are more tolerant of high temperatures, with respect to elasticity. However, I have yet to find any upper oil-temperature limits, specified for these engines. I envisage that any temperature limits, are likely to be dictated by the properties of the engine oil, rather than those of the aluminium alloy crankcase.

    Ironically, these engines run cooler than the VW 12/13/15/1600 Type 1, 2 & 3 engines, owing to the increased cylinder spacing (see Peter Noad, "Pacenotes", VW Motoring, August 1997, pages 62~64) and uprated cooling system, facilitating more efficient cooling. The spacing between the central axes of adjacent cylinders, is 112 mm and 124·5 mm, for the VW 12/13/15/1600 Type 1, 2 & 3 and VW 17/18/2000 Type 2 & 4 engines respectively; allowing greater air flow between adjacent cylinders of the latter engine. Cooling system air-flow rates, are quoted as 0·575 m3s-1 @ 4000 RPM and 0·800 m3s-1 @ 4600 RPM, for the VW 1600 Type 2 and VW 17/18/2000 Type 2 & 4 engines respectively.

    I and other owners of 1968~79 VW 1600 Type 2s, have found that when driving at about 55~65 MPH, on British motorways in summer, crankcase (i.e. sump) oil temperatures, are typically 110~120 °C and one individual, reported temperatures approaching 140 °C, for his newly reconditioned engine. 1972~83 VW 17/18/2000 Type 2 engines, are said to typically exhibit oil temperatures of about 90 °C, under similar motorway driving conditions. Engine-oil temperatures for both the 1968~79 VW 1600 Type 2s and 1972~83 VW 17/18/2000 Type 2s, plus other VWs, are likely to be much higher, when the vehicle is subjected to more severe operating conditions, such as high ambient temperature, high altitude, climbing a steep gradient, carrying a heavy payload or towing a trailer.

    In the USA, one 1976~79 VW 2000 Type 2 owner, reported that his engine-oil temperature was typically 110 °C, cruising at 60 MPH, when the ambient air-temperature was approximately 30 °C. In the past, I too have experienced summer, ambient air-temperatures of 30 °C or more, in central and southern Europe. Before fitting an oil-temperature gauge, I had noticed that under these conditions, my family's 1973 VW 1600 Type 2 engine, always smelled of hot, burnt oil, after a long high-speed run. In some inhabited regions of the World, within or close to the Tropics, daytime air temperatures, are close to 40 °C and in some of the inhospitable desert regions, may be as high as 60 °C.

    Another owner in the USA, reported engine-oil temperatures in the range of 115~125 °C, at an altitude of about 8000 feet (i.e. 2500 metres). In this latter case, the high engine-oil temperatures are probably attributable to a combination of climbing long, steep hills and the reduced cooling capacity of low-density mountain air.
    Last edited: May 10, 2009
  9. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet

    OIL TEMPERATURE continued

    At about 120 °C, conventional monograde and multigrade oils, start to break down chemically and oxidise. If oil is at 120°C in the crankcase, then it will be even hotter, elsewhere in the engine! Hence, it is hardly surprising, that the hot running, 1600cc, Type 2 engine, is often accompanied by the acrid smell of burnt oil, one associates with oil refineries. Similarly, it is probably due to the high running temperatures of these engines, that they seem to require a complete overhaul (including align-boring of the crankcase), after about 80,000 miles.

    Excessively high temperatures, will also lead to carbonised oil, encrusting the internal sufaces of the crankcase, valve rocker box covers and the oil galleries, plus formation of sludge, which in turn results in reduced cooling and consequent higher temperatures, plus potentially increasing problems of oil starvation. Fully-synthetic oils (such as Mobil 1) and semi-synthetic oils are more tolerant of high temperatures and have a lower volatility (see Anthony Curtis, "Fluid Formulae", Car Design & Technology, December 1991, pp36~44), limiting oxidation and reducing oil consumption. For these and other reasons, fully-synthetic oil, is used in the air-cooled, 6-cylinder, turbocharged and normally aspirated, Porsche 911 engines. Coincidently, in 1996 (see News Round, VW Motoring, September 1996, page 7), Porsche commenced filling all their new-car engines from the factory, with Mobil 1 synthetic oil

    When in 1986, I changed to using fully-synthetic, SAE 5W/50 Mobil 1 oil (now only available as either SAE 0W/40 or 15W/50), in our 1973 VW 1600 Type 2 engine, there was no more burnt-oil smell and oil consumption was reduced from 1 litre per 1,000 miles to 1 litre per 3,500 ± 500 miles; a significant improvement. However, one should be wary of changing to a synthetic oil, semi-synthetic oil or any other high-detergent oil, if there is any reason to suspect that there has been a build-up of sludge and deposits; possibly resulting from long-term use of poor quality, low-detergent oil and/or infrequent oil changes. If that is the case, disassembling the engine, followed by thorough internal cleaning and overhaul, would be appropriate, before it grinds to a halt.

    The underlying reasons for an overheating engine, which inevitably result in excessively hot oil (see Transporter Talk, Issue 40, April 1999, page 28), I have already documented in some detail. Some conditions which lead to overheating, may develop gradually, so that the engine's average running temperature, progressively increases with the passing weeks, months or years; discounting the effects of seasonal climatic variation. Such conditions, are likely to include the build up of sludge or carbon encrustation inside the engine, plus oil, dirt and litter (including plant leaves) outside the engine, some of which may be obscured by the cover plates.

    Crankcase, cylinder-barrel, cylinder-head and oil-cooler fins, clogged with oil & dirt, plus accumulations of leaves on top of the engine, beneath the coverplates, restricting air flow (see Tom Wilson, "How to Rebuild Your Volkswagen Air-Cooled Engine", HP Books, 1987, pages 66~67 and Peter Noad, "Pacenotes", VW Motoring, August 1997, pages 62~64), are well recognised. These tend to build up gradually and without an oil-temperature gauge, the tendency for the engine to run progressively hotter, may go unnoticed. Unless one observes the characteristic squealing noise of a slipping fan belt, one may be equally oblivious to gradual glazing of the fan-belt, which leads to increasing slippage and hence reduced fan speed.

    Less obvious, are the effects of underinflated tyres and binding brakes, wheel bearings or CV joints, which increase the vehicle's rolling resistance, which requires the engine to develop more power (hence requiring the dissipation of more heat), in order to propel the vehicle at the same speed. Bob Wallace (see Transporter Talk, Issue 30, August 1997, page 28) was surprised to discover, that the oil temperature, for his 1973 VW 1600 Type 2 engine, was typically about 10 °C cooler, after he renewed, greased and adjusted the front wheel bearings.

    Although I have no personal experience of rapidly increasing oil temperature, there are conditions where this could occur, so it would be useful, to supplement an oil-temperature gauge, with a warning light, activated by a break-on-fall, oil-temperature switch. Such accessory switches are available, but it is interesting to note that the VW Type 1 Beetle, with semi-automatic transmission, is equipped with oil-temperature switches rated at 120 ºC and 145 ºC to warn of over-heating transmission oil. I suspect that either one or both of these, could be used to sense engine oil-sump temperature!

    On one cold November day, C. John Hill (see Transporter Talk, Issue 55, October 2001, pages 27~28), noticed that oil temperature of his 1972 VW 1600 Type 2 engine, had risen rapidly to 120 ºC (approximately 15~20 ºC higher than the normal running temperature, for that time of year) and was still rising! Noticing this and the changed engine note, he pulled into a lay-by, where he discoverd that one half of the engine-bay, foam perimeter-seal had disappeared, which was presumed to have been sucked into the fan housing (a supposition which was later confirmed), where it drastically reduced the effectiveness of the cooling system.

    Few people regularly monitor their dashboard gauges, so it is fortuitous, that John noticed the increase in oil temperature, after a rise of only 15~20 ºC. A 120 ºC oil-temperature switch, linked to a warning light, plus a flashing light and/or buzzer system, would have been more likely to attract his attention! Hopefully, John's engine will not have suffered any ill effects, but I cannot help thinking that a cylinder-head temperature gauge and/or warning system, would have apprised him of the situation, much earlier. I'll wager that John is now thankful that he bought that second-hand oil-temperature gauge from me, back in September 1996!

    Although much has been said about the hazards of excessive oil temperatures, too low an oil temperature also has its attendent problems. It has been stated (see Bill Fisher, "How to Hot Rod Volkswagen Engines", HP Books, 1970, pages 89 & 92), that in order to minimise friction losses, condensation of acidic combustion products, varnish build-up, sludge formation and fuel dilution of the oil, oil temperature should ideally be maintained above 80 °C. During the warm-up period, it is recommended (see Peter Noad, "Pacenotes", VW Motoring, October 1997, pages 64~66) that engine speed should not exceed 3,000 RPM, whilst the oil temperature is less than 50 °C and maximum revs or full throttle avoided, until an oil temperature of at least 70 °C has been attained.

    If one frequently drives an air-cooled VW, during cold winter months, particularly for short journeys, it would be advantageous to fit a mains electric, immersion oil-sump heater (probably made by Fonas or Calix). This replaces either the oil-strainer plate, on the VW 12/13/15/1600 Type 1, 2 & 3 engines or the circular, dimpled sump plate (with two 10mm AF, M6 hex-head bolts) below the oil filler and dipstick, on the VW 17/18/2000 VW Type 2 & 4 engines and VW-Porsche 914-4 engines. These were commonly fitted to Swedish specification, air-cooled VWs, which I saw on sale at the Volkswagen agents in Västervick, back in 1982. Some may now be available, second-hand.

    There is the added note that if the oil does not reach 70 °C from cold, within about five minutes of start-up (presumably, under normal British climatic conditions!), then by some manner or means, the oil is being over-cooled. 'Over-cooling' may arise for a variety of reasons, which include:- malfunction, maladjustment or disablement of the cooling system's thermostatic control; fitment of an over-rated, after-market cooling system (see Peter Noad, "Pacenotes", VW Motoring, August 1997, pages 62~64), such as the increasingly popular Porsche 911 fan conversion; carburettor and/or inlet manifold icing; or oil is being diverted prematurely to either one or both of supplementary (if fitted) and standard oil coolers.
    Last edited: May 10, 2009
  10. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet

    OIL TEMPERATURE continued

    Diversion of oil to the standard oil cooler, is governed by the oil-pressure relief valve, which diverts oil to the oil cooler, as the oil temperature increases. The mechanism of this process (see Tom Wilson, "How to Rebuild Your Volkswagen Air-Cooled Engine", HP Books, 1987, page 40), is associated with the decrease in oil pressure as the viscosity decreases, which in turn occurs, because of the increase in oil temperature. Owing to the relationship between oil pressure and viscosity, premature diversion of the oil, to the standard oil cooler, may occur, when using oils possessing ultra low viscosity, at low temperature, such as SAE 0W/40, 5W/30, 5W/40 & 5W/50 (compared with the SAE 20W/20 and SAE 30, originally specified by Volkswagen, for winter use and summer use respectively, in temperate climates, like Great Britain); the significant number being the one before the 'forward-slash'.

    This is something that both myself and Neil Birkitt (former editor of the Bugpower and VW Motoring magazines) have observed, from our own experiences. The issue of which SAE viscosity ratings and other parameters, are most appropriate to the VW air-cooled engine, for the maintenance of optimum lubrication and cooling, are beyond the scope of this article, but I may cover it at some future date, if and when reliable data & information, become available!

    Neil Barstow, whose uprated 1978 VW 2000 Type 2 engine (140 horsepower, 2165 cc), was fitted with a Porsche 911 fan conversion, has told me that the engine is over-cooled and seldom if ever reaches normal operating temperature; often failing to rise above circa 60~70 °C. Given that a 3·2 litre Porsche 911 fan, was designed to cool a 230 horsepower engine, one should not be too surprised, but in principle, the problem may be overcome, by fitting a smaller drive pulley (known to be available in 130mm and 145mm diameter sizes) and/or a larger driven pulley, which drives the fan at a slower speed. Alternatively, use of a 5-bladed fan, in preference to an 11-bladed or 12-bladed fan, might be appropriate.

    During the two winter seasons I used our 1973 VW 1600 Type 2, the single Minnow Fish carburettor, with 'pancake' paper-element air filter on top, suffered from chronic icing (despite the 90W electric de-icing element) and the oil temperature rarely increased much beyond 50 °C; a condition to which I would have been oblivious, without the oil-temperature gauge. On one occasion, fuel dilution of the oil was so severe, the 'sump' contained about 1 litre of petrol, in addition to the 2·5 litres of oil! Carburettor icing is well known on air-cooled VWs, having a single carburettor (particularly those which have inadequate air pre-heating and/or inlet-manifold heating!) and has also been experienced occasionally with twin-carburettor installations, which many had thought to be immune.


    Although oil temperature gives a good indication of overall engine running temperature, it responds relatively slowly to sudden changes in engine running conditions, such as the loss or impairment of the cooling system, which typically arises as the result of V-belt failure (applicable only to the VW Type 1, VW 181 & 182 - Trekker or Thing, pre-1980 VW 12/15/1600 VW Type 2 and post-1979 Brazilian VW 1600 Type 2), or suction of debris (e.g. paper, leaves or cloth-rags) into the cooling fan inlet.

    When either of these occur, cylinder head temperatures increase rapidly; typically by a few hundred degrees, in less than a minute, as I know from experience! Such high temperatures, result in increasingly non-uniform temperature distributions and thermal expansion, ultimately leading to possible warpage and cracks, plus pulling the cylinder head studs out of the crankcase. If by this stage, the engine hasn't already siezed, the combined effect of these things, will themselves write off the engine.

    Even under normal running conditions, different parts of the engine, are at radically different temperatures and it is possible that either one or both cylinder heads may overheat, without causing a drastic increase in oil temperature. It is reported, that the strength of aluminium alloys (see Julius Mackerle, "Air Cooled Motor Engines", Cleaver Hume Press, 1961, pages 230~231 & 240~242), from which cylinder heads are constructed, diminishes significantly at temperatures in excess of 200 °C and that the temperature of the inner cylinder head surface, adjacent to the combustion chamber, should not exceed 235~250 °C. Localised temperatures in the hottest regions (typically in the neighbourhood of the exhaust valves and spark plugs), may at times be as much as 270 °C; albeit a short-term temporary condition.

    Chart of material strength versus temperature, for aluminium-alloy cylinder heads


    Plot of CHT versus RPM & MPH; said to be based upon actual data, obtained by Richard Atwell


    Under normal running conditions, one is recommended to avoid temperatures, in excess of 220 °C, because of possible temperature increases, arising from a lean air-fuel mixture and the consequent risk of detonation. It is largely the danger of exhaust valve overheating and the accompanying risks of valve failure and detonation (either of which can destroy an engine!), which limits the use of high compression ratios (the Porsche 911 is a noteworthy exception, probably associated with valve timing and/or high octane petrol) in air-cooled engines, owing to the higher operating temperatures.

    These are things which particularly need to be considered by VW Type 2 owners, contemplating the transplant of a more powerful engine (e.g. VW-Porsche 914-4 or VW 411 & 412, C.R. = 7·6 : 1, 7·8 : 1, 8·0 : 1, 8·2 : 1 or 8·6 : 1, dependent upon which engine), into their van, wherein it will tend to run much hotter, than it did when installed in the lighter, more aerodynamic donor car. As a rule, high cylinder-head temperatures should be avoided where possible, if for no other reason, than to maximise cylinder head lifespans, by minimising the likelyhood of crack formation and/or permanent distortion; especially at the seal between the cylinder head and the cylinder barrel.

    Several years ago, whilst cruising along the M25 motorway, at 60 MPH, in my family's 1973 VW 1600 Type 2, I glimpsed the illumination of the ignition (i.e. generator) warning light. Fearing the possibility of a broken V-belt, I coasted to a halt on the hard shoulder and immediately switched off the engine, which saved it from any damage. In those few moments, the cylinder head, external surface temperature (the internal surface temperature would have been much greater!), had increased from 100°C to nearly 200°C.

    Whether or not I would have noticed the movement of the gauge needle as the temperature increased, is open to debate, but having been alerted by the illumination of the ignition warning light, the gauge readings confirmed to me that stopping the engine was imperative! On this occasion, it turned out that not only had the V-belt failed (all I found were its fragmented, charred remains), but the alternator which I had fitted about 9,000 miles earlier, had completely siezed solid; it being impossible to turn the shaft, even with a very long spanner. Keith Herbert (see Transporter Talk, Issue 55, October 2001, page 36) and Mark Davis, fellow members of the VW Type 2 Owners' Club, similarly experienced dynamo-shaft bearing failure, on their VW 1600 Type 2s, whilst on holiday in France and Portugal respectively.

    James Horsley (see Star Letter, VW Motoring, January 1999, page 62) and the Reverend Paul MacCarty (see Transporter Talk, Issue 46, April 2000, pages 39~40) were not so fortunate, with their VW 1600 Type 2 engines. To quote James's words, "Something had been drawn into the fan and caused the engine to cook itself". Paul reported that, "The engine had died, absolutely" and "The J-cloth was spread neatly over the cooling fan vanes", the cloth having been used earlier to clean the engine bay and left on top of the battery. All too often, I see old rags deliberately left in the engine compartment of people's vans, ready to wipe the oil dipstick.

    In both cases, debris had obstructed the cooling system air-flow, causing the engines to rapidly overheat and sieze. The generator would still be functioning, being driven by the V-belt, so the ignition warning light would not have illuminated. Only a cylinder-head overheat switch & warning light, plus possibly a cylinder-head temperature gauge, would have warned them of impending doom. Judging from the various tales of woe, which appear all too regularly in Transporter Talk, VW Motoring and other VW magazines, the aforementioned cases, are only the tip of the iceberg!
    Last edited: Jul 9, 2011
  11. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet


    With the exception of pre-1971 'upright-fan' engines (i.e. VW 12/13/15/1600 Type 1 & 2), with one-piece oil coolers inside the fan housing, it is probably assumed that both cylinder heads, of VW air-cooled engines, run at approximately the same temperature. Personal experience with a 1973 VW 1600 Type 2, having a 'dog-house' cooling-fan housing, with two-piece oil cooler and twin-port engine, with single carburettor and three-piece inlet manifold, would suggest otherwise!

    I discovered during some routine maintenance, that when the engine was fully warmed up and running at idle, the right-hand inlet manifold branch (aluminium alloy casting), to cylinders 1 & 2, was too hot to touch bare handed, for more than an instant, whilst in contrast, that to cylinders 3 & 4, on the left-hand side, could comfortably be grasped for some time. What might have lead to such a large disparity in temperature, I am not sure, but I have a few hypotheses. In general, there are many possible reasons; including dissimilar cylinder heads (my pet theory, having previously replaced a damaged one – potentially affecting volumetric efficiency, compression ratio, piston squish clearance and combustion characteristics), uneven fuel distribution and unequal cylinder head & barrel cooling (hampered by oil, dirt or debris).

    Ironically, I had some years earlier, fitted the temperature sender unit, of my cylinder head temperature gauge, to the left hand cylinder head; having previously heeded the advice, that cylinder 3, was the hottest running (allegedly!), on these engines. It was with this configuration, that I experienced my breakdown, with the siezed alternator. I have since wondered, what temperature was finally reached, by the right-hand cylinder head! Being more aware these days, of the various factors which can influence engine running temperatures and overheating, I have now made provision for separate temperature gauge sender units, on both cylinder heads (connected to a single gauge via a double-pole, changeover switch), of our 1911cc, VW 17/1800 Type 2 & 4 hybrid engine and ultimately intend to fit overheat switches for a warning light.


    In common with cylinder-head temperature, exhaust-gas temperature can change very rapidly, but unlike the former, it should be relatively insensitive to engine load, provided air-fuel ratio remains constant, giving a direct indication of combustion chamber conditions, such as air-fuel mixture ratio; particularly a lean fuel mixture, leading to increased exhaust-gas temperature, which is a prelude to detonation. Exhaust-gas temperature, is measured using a pyrometer, whose sender probe is inserted into the exhaust-gas stream, through a threaded boss, welded onto the exhaust system, as close to the cylinder head exhaust ports, as is practical.


    If one were obsessed with engine monitoring, one could even use an ambient air-temperature gauge, with -25~0~40 °C range, to monitor the temperature of the engine compartment, incoming combustion air (ambient and pre-heated) and inlet manifold(s), to obtain information about conditions pertaining to optimum power, economy and carburettor icing, plus the possibility of detonation and engine overheating. Such temperature monitoring, would be particularly important, where a supercharger or turbocharger and intercooler conversion, has been fitted. When monitoring engine associated air temperatures, in excess of 40 °C, it might be advisible to switch over to a "water-temperature" gauge, having a 40~120 °C range, which appears to share the same sender unit options!


    Traditionally, the vacuum gauge has been used as an aid to economical driving, whereby one adjusts the position of the accelerator pedal, to give the greatest reading of vacuum, for a given load. However, it is also a useful instrument for diagnosing a variety of engine conditions and faults, such as:- a clogged air filter; obstructed or damaged exhaust system; air leak at the manifold, carburettor or throttle body gaskets; incorrect valve timing; sticking or leaking valves; worn valve guides; weak valve springs; worn piston rings; retarded ignition timing; a gasket leak between adjacent cylinders (unlikely on an air-cooled VW engine); and more comfortingly, an engine which is in good condition and well tuned.

    In general, diagnostic readings are taken with an engine at normal operating temperature and running at idling speed, which are described as follows; the gauge illustration numbers, corresponding directly to the numbered sections. At high altitudes, the readings will be lower, owing to the decrease in atmospheric pressure.

    1. An engine in good condition, should give a steady reading of about 17~22 in.Hg. On the whole, the higher the reading the better, but the maximum possible reading for a perfect, run-in engine, will depend on a number of design factors, which include such things as:- valve timing (opening, closing, duration and overlap); plus inlet manifold, air-filter housing and exhaust system flow resistance.

    2. Confirmation of good conditon, may be obtained by blipping the throttle, which should result in the reading dropping momentarily to about 2 in.Hg, rising to approximately 25 in Hg and then settling back to 17~22 in.Hg.

    3. A steady, higher than normal reading, indicates a clogged air filter element (wire mesh gauze, in an oil-bath air cleaner) or restrictive air-filter housing. How high the reading is, depends upon the degree of restriction or clogging.

    4. An obstruction in the exhaust system or a damaged pipe, will give a normal reading on start-up, but will soon drop to 0~5 in.Hg; dependent upon the extent of the damage or obstruction.

    5. Air leaks at the inlet manifold, carburettor or throttle body gasket, will result in a steady low reading below 5 in.Hg. How low, is dependent upon the extent of the leak. Exceptionally, a similar effect occurs with a porous inlet manifold casting; a phenomenon which was encountered by an aquaintance of mine.

    6. Incorrect valve timing is usually indicated by a steady reading of 8~15 in.Hg. A problem of this type, does not arise spontaneously or progressively, but occurs because a camshaft has been incorrectly installed; either as a result of the timing gear index mark having not been aligned with the two marks on the crankshaft gear, or the camshaft has had its timing gear incorrectly fitted. Fortunately this problem rarely occurs on air-cooled VW engines, but is more likely on other engines, whose camshafts are belt or chain driven; for which setting the valve timing is more involved.

    7. A periodic decrease of 2~5 in.Hg below normal idling vacuum, suggests one or more leaking valves; probably caused by insufficient valve tappet clearances or in extreme cases, valves being burnt. Alternatively, one or more spark plugs may be misfiring.

    An irregular, periodic decrease of similar magnitude, indicates a sticking valve or valves. If the introduction of a little penetrating oil ( whether this is practical in all cases, is questionable!) into the inlet manifold, appears to temporarily solve the problem, then this is confirmation of sticking valves.

    A steady lower than normal reading, of this magnitude, suggests the possibility of retarded ignition, which might be caused by incorrectly set ignition contact breaker points. Alternatively, such a reading might be attributable to worn piston rings; requiring confirmation, as outlined in section 11.

    8. Worn valve guides (dependent upon the number of guides which are worn) results in a rapidly vibrating reading of 14~19 in.Hg, which increases in frequency and dcreases in amplitude, as one increases engine speed. This condition is one to which the air-cooled VW, flat-four engine, is particularly prone, owing to the lubrication problems associated with the high running temperatures and the almost horizontal valve orientation.
    Last edited: May 10, 2009
  12. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Compiled & Written by Nigel A. Skeet


    9. The existence of weak valve springs, causes the gauge needle to swing back and forth, when accelerating from idle; the extent of the swing being dependent upon engine speed.

    10. A regular swing of the gauge needle, between about 5 in.Hg and 19 in.Hg, would suggest a gasket leak between adjacent cylinders. Given the nature of their construction, this would be virtually impossible with an air-cooled VW engine, but may afflict some others. So far, I have yet to find any documented information about what vacuum readings would result from a leak to the external environment, via the cylinder head to cylinder barrel seal; a condition to which the air-cooled VW engine is prone, particularly if the cylinder heads have distorted, as a result of overheating.

    11. A steady reading below normal, suggests either retarded ignition timing (see section 7), or worn piston rings, pistons and/or cylinder bores. To confirm which, accelerate the engine to about 4000 RPM (for which a rev counter would be useful!), then close the throttle quickly. The gauge should momentarily read about 3~7 in.Hg above the normal; anything lower than this, confirming that worn piston rings, pistons and/or cylinder bores are evident.


    In the past, when my family's 1973 VW Type 2 was fitted with the 1600 engine, a dashboard mounted vacuum gauge, would have been useful, on at least two occasions; once to forewarn me of an increasing problem with worn valve guides and in a separate incident when the ignition timing was becoming progressively more retarded.

    In the first case, I had observed a developing problem of crankcase pressurisation (inferred from an increasingly oil-fouled, paper element air filter) and increased oil consumption, despite the maintenance of good cylinder compression pressures. The existence of worn valve guides was finally confirmed, using a hand-held vacuum gauge (i.e. Gunson's low-gauge). Owing to their effect on inlet manifold vacuum, the worn valve guides, were also adversely affecting vacuum ignition advance, which has a significant influence on fuel economy, under part throttle, cruise conditions.

    The other incident arose, whilst on holiday in Northern France, when the ignition contact breaker points' plastic heel (i.e. cam follower), experienced a high wear rate, owing to roughening of the distributor cam lobes. This resulted in the progressive reduction of the points gap and retardation of the static ignition timing, which resulted in a sooty exhaust pipe, plus deteriorating performance and fuel economy.

    Had the vehicle not been fitted with an FCD (i.e. frequency controlled dwell) electronic ignition system, the engine would also have started to misfire as the points gap diminished, owing to the reduction in dwell angle. Fortunately, with the FCD system, I could maintain satisfactory performance, by readjusting the points gap and resetting the static ignition timing, on a daily basis, until I had the opportunity to remove the ignition distributor and polish the cam using successively finer grades of 'wet & dry' abrasive paper. Why the cam originally became roughened, I never discovered!


    Although not a standard fitment on VW air-cooled engines, supercharger and turbocharger (more specifically a turbo-supercharger) conversion kits, have been available for at least the past three decades. Both devices increase the overall available power, by forcing a larger mass of air into the engine, but a turbocharger has the added advantage, that for a given engine speed, it further increases the boost pressure, as altitude increases (see Alan Allard, "Turbocharging & Supercharging", Patrick Stephens Ltd., 1982), hence compensating for the associated reduction in atmospheric pressure and air density.

    This is one reason why they have commonly been used on piston-prop, aero-engines (e.g. Douglas DC3 / C47 'Dakota' and Boeing B17 'Flying Fortress', to name but a few), as Robin Taylor will doubtless recall from his flying days. Arthur Barraclough would undoubtably have appreciated this advantage (see Simon Holloway, Transporter Talk, Issue 18, August 1995, p20) of a turbocharger, had one been fitted, whilst crossing the Himalayas, in his 1970 VW Type 2 and which Ralph & June Pettitt may have noted during their extensive World travels, in their 1986~92 VW 1600 Type 2 Turbo-Diesel Syncro!

    As the engine speed increases so does that of a supercharger or turbocharger, enabling it to generate higher boost pressures. Normally, turbocharger boost pressure is limited to some pre-determined maximum, by allowing a proportion of the engine exhaust gases to bypass the turbocharger, using a device known as a waste gate. If the waste gate malfunctions (hopefully in failsafe mode) then boost pressure will be further limited, reducing maximum available power. However, if the waste gate fails to open properly, boost pressure can exceed safe limits, leading to excessive combustion chamber pressures and temperatures, which in turn leads to destructive detonation.

    When rapidly compressed, by either a supercharger or turbocharger, air increases in temperature and in addition, the air temperature is further raised by a turbocharger, as a result of heat transmission, from the hot exhaust gases, driving the turbine. By cooling the compressed air by means of an intercooler (a cross-flow, air-to-air heat exchanger), the volume of the air contracts, resulting in increased air density, so even more air flows into the combustion chamber, further increasing power. Reducing the air temperature by this means, also reduces the risk of detonation. However, if the cooling efficiency of the intercooler is reduced by fouling or otherwise, the combustion chamber pressures and temperatures will increase, hence increasing the risk of detonation.

    In addition to waste gate malfunction, there may be a loss in boost pressure, as the result of general wear and tear, of either a supercharger or turbocharger. In the case of the turbocharger, this is not surprising, considering that at full boost, they often run red hot and typically at speeds of 100~150 thousand RPM. At low engine speeds there is little if any boost, so relative to atmospheric pressure, the inlet manifold is subject to a partial vacuum rather than a positive pressure; the engine behaving like an old generation, low-compression engine, under these conditions.

    To monitor the running conditions of a supercharged or turbocharged engine and detect any deviation from normality, in the boost pressure, at any given engine speed, one requires a boost gauge, typically with a range of -1·0~1·5 BAR or -1·0~2·0 BAR. To some extent, the boost gauge might also aid in the diagnosis of some conditions, for which a vacuum gauge would be used, with a normally aspirated engine.
    Last edited: May 10, 2009
  13. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Another under-rated instrument, is the rev counter (otherwise known as a tachometer), which is typically only fitted to performance and luxury cars, plus commercial diesels. However, the rev counter gives useful feedback with regard to over-revving or under-revving and whether the engine is being operated within the optimum rev range, for reliability, longevity and fuel economy. Rev counters fitted as standard to some diesel engined boats and commercial vehicles, incorporate a green sector, showing the optimum rev range.

    Owners of the 1968~83 VW 1600 Type 2, will be familiar with the need to rev to full power and beyond (4,000~4,500 RPM) in 3rd gear, before changing up to 4th, when overtaking (not my favourite passtime!) and/or hill climbing. This need arises, because the 1600 engine is chronically under-powered (47~50 DIN horsepower @ 4,000 RPM) and the large step (i.e. multiplication factor of 1·54) between 3rd and 4th gears. This highlights the need for a 5-speed or 6-speed transaxle, with more closely stepped ratios, which I shall discuss in another article.

    To prevent over-revving, Volkswagen in their 'wisdom', fitted a centrifugal cut-out (i.e. governor) type, ignition rotor arm, which shorts the HT ignition pulses to earth, when the engine attains 4,500 RPM. The absolute maximum rev limit, for the VW 12/13/15/1600 Type 1, 2 & 3 engines, is 5,000 RPM. The 1972~83 VW 17/18/2000 Type 2 engine, is also fitted with a cut-out type rotor arm, which operates at 5,400 RPM, but this engine, in common with the VW 17/18/2000 Type 4 (VW 411 & 412 and VW-Porsche 914/4) engines, can safely be revved to a maximum of 6,000 RPM, in unmodified form.

    Ignition cut-out, is characterised by violent juddering of the whole vehicle, arising from induced vibration of the engine and transmission., which is likely to cause more damage than merely over-revving the engine by 500 RPM or so. This situation can be avoided, by replacing the cut-out type rotor arm with the conventional type, plus fitting a rev counter and/or adjustable, electronic, smooth-cut rev limiter, which are also incorporated into some after-market electronic ignition systems, such as the Microdynamics Formula 1, FCD system, fitted to my family's 1973 VW '1600' Type 2.


    Although more commonly of interest to the automotive engineer or professional engine tuner, rather than the average motorist, air/fuel ratio is an important parameter with regard to exhaust gas emissions, optimum power & fuel economy, plus forewarning of excessively lean mixtures which leads to rapid overheating and potentially destructive detonation. For the properly maintained, factory standard specification engine, excessively lean mixtures should not present a problem. However, even for such vehicles as these, the abilty to monitor air/fuel ratio might be useful, if it is driven at widely varying altitudes.

    These days, a significant proportion of VW air-cooled engines have been modified in some way. Such modifications range from the simple bolt-on variety which requires no dismantling of the engine itself, upto a complete rebuild using one or more specialist aftermarket components, such as cylinder heads, cylinder barrels & pistons, crankshaft & connecting rods, camshaft, etc. Even the increasingly popular bolt-on modifications, such as substituting an aftermarket extractor exhaust system, fitting high-ratio rockers, alternative single or twin carburettors and/or low-loss air filter, can affect the engine's volumetric efficiency and hence the air/fuel ratio under varying conditions of engine speed & load.

    Maximum power, minimum fuel consumption and optimum exhaust emissions, are attained at differing air/fuel ratios.

    MSD Rich/Lean indictor, PN 8933 gives information about whether the engine combustion mixture is on the rich or lean side of the stoichometric 14·7 : 1 ratio, reviewed in What's New – Now That's Rich, VW Trends, November 1995, p21. Uses a titania heated oxygen sensor which installs into the exhaust system. Green light mixture is rich. Red light on mixture is lean

    Air/Fuel monitor which reads like a gauge, ranging from ratios of 12 : 1 to 17 : 1 and the ideal stoichometric 14·7 : 1 ratio, from CB Performance Products. Mixtures weaker than 18·4 : 1 (i.e. lamda l = 1·25) can be ignited by a flame, as employed in a modern stratified charge engine, but not by a spark from a spark plug.


    In a normally running engine, the fuel-air mixture is ignited by the electric spark from the spark plug, causing a flame front to propagate through the mixture, at about 30 metres per second, until all (ideally!) the fuel is burned. Under some circumstances, heat radiated by the already burning fuel or other heat sources, causes a portion of the unburnt fuel-air mixture (known as the end gas), remote from the flame front, to heat up to its ignition temperature, which spontaneously ignites and burns in an uncontrolled and explosive manner.

    This phenomenon, known variously as detonation, knock, spark knock, pinking or pinging, is potentially very destructive, which in extreme cases can burn or blast holes through the piston crowns, break piston rings, damage valves and deform the main bearing bores, plus any consequential damage; effectively reducing an engine to scrap metal. Even long-term, light detonation, will tend to result in more rapid wear of the pistons, piston rings and cylinder bores, plus increasing fuel consumption.

    In a standard production engine (installed in the intended vehicle application), detonation usually occurs for one or more of the following reasons (see Bill Fisher, "How to Hot Rod Volkswagen Engines", HP Books, 1970, p22) :- petrol octane rating (i.e. RON or MON or their arithmetic average) is too low; over advanced ignition timing; faulty vacuum advance mechanism; too lean a fuel-air mixture; engine overheating or running hotter than normal; spark plugs are of too high a heat range (i.e. wrong grade); exposed spark plug threads (used too thin a sealing washer or mistakenly fitted 19mm instead of 12mm reach spark plugs, to a VW 12/13/15/1600 Type 1, 2 or 3 engine!?); excessive oil consumption (burned rather than leaked!); excessive carbon build-up in the combustion chamber or the engine is overloaded (e.g. hill climbing or accelerating in too high a gear).

    In the case of 'non-standard' engines (i.e. engine has been modified or transplanted into another vehicle type), other contributory factors which should be considered, are:- too high a compression ratio for the available octane rating (may be countered to some extent by reducing the piston squish clearance to 1·0~1·3mm and/or ceramic coating of the combustion chamber surfaces, valve heads & piston crown and/or water injection); inappropriate ignition advance curve (i.e. over advanced); plus sharp edges to the valve heads (especially the exhaust valves) and the combustion chamber edges (particularly near the cylinder barrel sealing surfaces).

    Detonation is characterised by a distinctive, metallic pinging sound, typically in the 7·5~10·0 kHz frequency range (dependent upon cylinder bore), but unfortunately, it is not always audible (even less so, on rear-engined vehicles), so may occur unbeknown to the driver. Modern petrol engined vehicles, fitted with sophisticated engine management systems (e.g. Bosch Digifant), are equipped with knock sensors, which detect the characteristic vibration frequencies, associated with detonation and retard the ignition timing; enabling the spark advance to be optimised (see William B. Ribbens, "Understanding Automotive Electronics", Newnes, 5th Edition, 1998, pp243~250), to give the greatest engine torque, for the prevailing engine running conditions.

    The hot running, VW air-cooled engine, is particularly sensitive to incorrect ignition timing and/or advance characteristics, plus other factors which promote detonation, so an instrumentation system, comprising one or more knock sensors (probably one on each cylinder head), appropriate electronic circuitry and a warning light or buzzer, would be particularly useful. It has been said that on some engines, the opening and/or closing of the valves, may give rise to vibration frequencies, similar to those which are characteristic of detonation, so any electronic circuitry, might need to discriminate between signals, according to their timing relative to each other, the firing of the spark plugs and/or the rotation of the crankshaft.
    Last edited: May 9, 2009
  14. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    I am still researching the practicality of such a system, so fellow owners, with knowledge of modern automotive engineering or signal processing, may wish to cooperate in this venture. It is probable, that most, if not all of these issues, have already been addressed, in the design of the Bosch Digifant system, fitted to the current Mexican built VW 1600 Beetle and some of the water-cooled, flat-four, petrol-engined, 1983~92 VW Type 2s. This being the case, it should be possible to adapt part of that system's circuit design. Alternatively, such a circuit appears to have already been designed; illustrated at the following Internet website:


    A detonation warning system, would have been invaluable to Theresa & Jonathan Hewat (see "Overland and Beyond", Roger Lascelles, 5th Edition, 1981), during their 90,000 mile World tour, in a 1972 VW 1700 Type 2 motorcaravan. Despite the relatively low, 7·3:1 standard compression ratio, which enabled the van to run on 91 RON octane petrol, they had the misfortune, to fill up with petrol of a particularly low octane rating (probably 83 RON!), somewhere in South America. Just this one fill-up, caused such severe engine damage, that before they could continue their journey, the engine had to be rebuilt, which involved renewing the pistons, plus whatever else!

    A similar fate, befell Christian Figenshou's, South African assembled, 1975 Brazilian CKD kit, VW 1600 Type 2, Fleetline Kombi (an odd hybrid of the 1964~67 & 1968~79 VW Type 2s!), during his recent 2002 Cape Town to Cairo expedition (see Christian Figenshou, "Capetown to Cairo in a Vintage VW Bus: Part 2", Volkswagen Camper & Commercial, Winter 2002 – Issue 9, pages 38~42). When supposedly buying 90 RON petrol (i.e. gasoline) during a fuel fill­up in Egypt, it is thought that he was either mistakenly supplied with 80 RON petrol or petrol which had somehow been adulterated (i.e. contaminated with some other substance, such as diesel or paraffin).

    This combined with a long ascent from sea level, to an altitude of 1,750 metres (i.e. 6,000 feet), over a distance of 250 km, caused severe detonation and overheating, leading to major damage to the engine, necessitating replacement of one cylinder head a day later, followed by an engine rebuild two days after that, using worn-out, second-hand pistons & cylinder barrels (all that were available), somewhere in Turkey. I vaguely recall warning Christian of the perils of low grade fuel, prior to his departure from South Africa, but even the best informed can suffer misfortunes!

    If these episodes seem rather remote from home, remember that two-stroke engines, which were and may still be, in common use in parts of Eastern Europe, run on 83 RON petrol; often with a proportion of pre-mixed lubricating oil, already added. Either the wrong fuel in the wrong storage tank or confusion about forecourt petrol pump identity, could lead to your VW engine, receiving a 'lethal' dose, of low octane petrol or even diesel fuel (10 RON octane rating!). Similar problems (albeit less drastic) may arise, if the engine suffers a high rate of lubricating oil consumption (i.e. burned rather than leaked), which like the addition of diesel, has the effect of reducing the petrol's octane rating.

    Recently (see Isabel Gompertz, "Cars Stranded in Fuel Mix-up", Castle Point Evening Echo, Tuesday 25th March 2003, pages 1~2), there was an incident at my local (i.e. Canvey Island, Essex, Great Britain) Safeway supermarket filling station, whereby diesel fuel had mistakenly been discharged, into the underground storage tank, for unleaded petrol (i.e. gasoline). The local newspaper reported, that several cars had been affected and that Safeway had accepted liability for any damage resulting from the mistake!

    Previously, it had been reported in a national newspaper (see Sean Poulter, "Breakdowns Soar in the Switch from Leaded Fuel", Daily Mail, Friday 17th December 1999), that dispensing the wrong fuel into vehicle's fuel tanks, was becoming increasingly common, owing to the lack of a consistent colour-coding system, for filling station forecourt fuel pumps. It was also stated that "diesel fuel in a petrol engine, can cause a sudden and devastating seizure". In the USA, it is now common practice to label petrol pumps with an octane rating, which is the arithmetic mean of RON and MON; this being claimed to be about 4 points lower than RON, in most cases.


    Pre-ignition, as the name suggests, occurs when the fuel-air mixture ignites before the spark plug fires, caused by 'hot-spots' on the surface of the combustion chamber (see Bill Fisher, "How to Hot Rod Volkswagen Engines", HP Books, 1970, page 22), which are typically associated with carbon deposits or sharp edges, particularly in regions which would normally be hotter than average. Carbon deposits can arise through habitual short distance driving, overly rich fuel-air mixture or excessive oil consumption. Sharp edges, associated with exposed spark plug threads, exhaust valve-head margins and combustion chamber edges, are acknowledged culprits!

    In general, pre-ignition causes thermal damage to pistons and valves, plus physically damaging the valve springs. In extreme cases, pre-ignition can lead to the explosive collision of two separate flame fronts, much akin to detonation. The likelyhood of pre-ignition is promoted by many of the factors, which also lead to detonation; these being over-advanced ignition timing, excessive engine running temperature and a petrol octane rating, which is too low. Note that an engine which is observed to run-on (sometimes called over-running or dieseling), after the ignition is switched off, probably suffers from pre-ignition, under normal running conditions!

    In contrast to detonation, pre-ignition is characterised by low frequency noise, which is more difficult to detect in a running engine, because of the many other sources of similar noise, which are present. At this juncture, I know of no readily available pre-ignition, detection instrumentation, which might be incorporated into a warning system. However, I have been told that the system used to detect detonation, should also be able to detect pre-ignition; albeit with some additional electronic circuitry.
    Last edited: May 9, 2009
  15. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    Although an altimeter or air pressure gauge, might seem to be a somewhat strange instrument, to have in a motor vehicle, an altimeter was regarded as essential, by the legendary Arthur Barraclough (see Simon Holloway, "Van of the Year :- BWR 4H - Arthur Barraclough", Transporter Talk, Issue 18, August 1995, p18), whose much modified 1970 VW Type 2, had travelled far (nearly 220,000 miles) and crossed several mountain ranges including the Himalayas; or so Arthur told me during our correspondence. Some, or all Mitsubishi Shogun, 4-wheel drive vehicles, have an altimeter fitted into a three-position, accessory instrument pod, on top of their dashboards. Information about altitude, can be obtained from some GPS and satellite navigation systems.

    Altitude directly affects both ambient air density and pressure, which in turn influence an engine's fuel-air ratio, so they are not just of academic interest to the mountain traveller. The fuel-air ratio of an engine, whose carburettor is adjusted for low altitudes, close to sea level, will become progressively richer, as altitude increases. Hence, if one has information about altitude (many altimeters operate on the basis of changes in atmospheric pressure) or air pressure, then in principle, one can readjust the fuel-air ratio to compensate.

    Whether it would be necessary to adjust the fuel-air ratio, on vehicles equipped with electronic fuel injection, such as the Bosch D­Jetronic, L-Jetronic or Digifant systems, I am not sure, but to a greater or lesser extent, all of these systems take some account of variation in atmospheric pressure. Sadly, any readjustment of the fuel-air ratio, will have relatively little effect, on the reduction in power, attributable to the reduced air density. The only truly effective means, of overcoming power loss with increasing altitude, is to fit a turbocharger, whose boost pressure naturally increases, to compensate for the reduction in atmospheric pressure and air density.

    In addition to its effect on fuel-air ratio and engine power, increasing altitude also reduces inlet manifold vacuum readings and cylinder compression pressures. Hence, if one is using either of these for diagnostic purposes, or just generally monitoring the running of the engine, then this needs to be borne in mind.


    The instrumentation mentioned so far, has dealt exclusively with the running of the engine. However, the electrical system is also prone to faults, which might cause a breakdown, less than optimum performance and more besides; about which, little if any information is provided, by the standard ignition warning light.

    Even when the ignition warning light is extinguished, one cannot be sure that the battery is being charaged; only that the difference in voltage between the battery and the generator (dynamo or alternator), is insufficient to cause a 12 V bulb to glow. In fact, the battery may even be discharging! To satisfactorily monitor the behaviour of the electrical system, one needs to measure both voltage and current flow; necessitating a voltmeter (sometimes known as a battery condition meter) and an ammeter.

    In order to maintain the health of a lead-acid car battery, it is important that it should be fully recharged; ideally requiring a generator voltage of about 13·9~14·3 V (see Tony Tranter, "Automobile Electrical Manual", Haynes Publishing Group, 1983, page 57). If the applied voltage is too low, full charge capacity will never be restored, resulting in the battery charge capacity and maximum discharge rate, progressively deteriorating, owing to sulphation of the plates. The principal purpose of the voltmeter, is to ensure that the generator's voltage regulator, is functioning correctly.

    Some batteries are marked with the warning, that the external charging voltage, applied across the battery terminals, by the generator or mains charger, should not exceed 14·4 V. Severe overcharging, causes the battery to overheat, boiling off the sulphuric acid and possibly buckling the plates which may lead to an internal short, in one or more cells; rendering the battery unserviceable. Sulphuric acid vapour can also result in extensive corrosion, in surrounding body panels, as some owners have found to their cost.

    Even if the optimum charging voltage is applied, it is not certain that the battery is being adequately recharged. This may arise if there are significant voltage drops in the cables or connections (very likely if vehicles are more than a few years old and haven't been adequately maintained or the cable connectors are merely crimped and not soldered), or the battery is nearing the end of its useful life, owing to sulphation or an internal short.

    Under some conditions, the battery may even be discharging; supplementing the current provided by the generator, to meet high electrical loads, which typically occur, when driving in slow moving traffic, in cold, damp and dark conditions. The only way to be sure that the battery is being charged, is to have an ammeter in the circuit, directly between the generator and the battery, which will indicate the instantaneous rate of charging or discharging, but not the total quantity of charge stored. A remote-shunt ammeter (made by VDO, Lucas and others), which requires only light-duty cable, is the most appropriate to the rear-engined VW, but the more widely available, conventional internal-shunt ammeter, may also be used, albeit in conjunction with several metres of heavy-duty cable.

    As a 12V battery approaches a fully charged state, the voltage across its terminals, may rise to as much as 15·0~16·2V, dependent upon the applied voltage of the charging source. When the charging current ceases (i.e. the generator or battery charger has ceased operating), the battery terminal voltage quickly falls to about 12·6V. As the battery discharges at a nominal rate (effect of high current load is discussed later, in relation to starter motor operation), the terminal voltage falls rapidly from 12·6V to 12·0V, at which it remains for most of the discharge period, until close to the fully discharged condition, it rapidly diminishes to about 11·8V. Hence, a voltmeter only gives any indication of the charge stored by a battery, when it is either close to the fully charged or fully discharged conditions.


    The voltage values cited in the preceeding paragraph, assume a battery temperature of 25°C; the voltage diminishing as temperature decreases (a topic in electro-chemistry, covered as part of B.Sc. Chemistry & Physics). Before starting their engines in winter, Russian motorists allegedly turn on their headlamps for a short period, so that the current draw, warms the battery, thus increasing the voltage and current available to the starter motor; or so I've been told. It sounds plausible, but I have yet to try it myself!

    From the preceeding discussion, it is apparent that under most circumstances, a voltmeter and ammeter, only give an instantaneous view of prevailing conditions in the electrical system; any assessment of the state of battery charge, being reliant upon one's recall, of the history of charging and discharging, during the journey, which inevitably tends to be rather subjective. To measure the extent of total battery charge, would require some electronic circuitry, to integrate the charge flow rate with respect to time (i.e. electronics applied to integral calculus), which is readily achievable these days.

    Battery suppliers assess battery condition, when fully charged, by conducting a high-rate discharge test, simulating the high current discharge of circa 100A, which occurs when running a typical starter motor. If one conducts a similar test, by observing the decrease in voltage reading, as the engine is turned over on the starter motor (typically 0·5~0·6 kW rating, for a VW Type 2), one might reasonably expect a reading of about 11V with a new battery, which will progressively diminish with age, as the battery's internal resistance increases, owing to sulphation and other processes.

    If a reading as low as 9V is observed, then the battery is nearing the end of its useful service life. Sulphation may be inhibited by adding to each battery cell (preferably when new), about one heaped teaspoon, of an analytical chemical reagent, known as EDTA (i.e. Ethylene Diamine Tetra-acetic Acid or its Di-sodium salt), which I have done since the mid-1980s. My family's car batteries typically last about 6~8 years. The battery of my father's Ford Sierra XR4x4, lasted an incredible 13 years!
    Last edited: Jun 10, 2009
  16. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation

    Whilst on holiday in Sweden in 1982, with my family's 1973 VW 1600 Type 2, we suffered two breakdowns, owing to failure of the dynamo and voltage regulator, on two separate occasions. In the first case, when the dynamo failed, I was warned that something was amiss, by sudden illumination of the ignition warning light, which after inspection of the V-belt, prompted us to visit a Volkswagen agent in Västervik, the next town, where the dynamo was replaced.

    When the voltage regulator burned out some days later, the ignition warning light did not illuminate at any stage, despite a functional bulb. The first hint of this problem, was when the engine began to judder, in a way which was reminiscent of a faulty cut-out type rotor arm, shorting the HT ignition pulses to earth, at low engine revs, which I had experienced on holiday in Belgium , some years earlier. Having a burnt out voltage regulator, the battery wasn't being charged, so the ignition system and the headlamps (daytime use is compulsory in Sweden, unless one has special daytime running lights), were running on the battery's reserve capacity, leading to a drop in supply voltage.

    Having stopped the vehicle on a steep uphill gradient (not the best of places!) and found the rotor arm to be okay, I attempted to restart the engine, but discovered that the battery was virtually flat. Not possesing a starting handle facility in those days (later fitted, owing to sporadic episodes, of the dreaded, 'dead starter motor syndrome'), I was obliged to undertake a rolling start, downhill, in reverse gear; a procedure which I would not generally recommend.

    By driving with the headlamps switched off, there was sufficient battery voltage available, to run the ignition system, for several more miles, until we reached Vetlanda, the next large town, where there was a Volkswagen agent. Had we been driving in a country where daytime headlamp use was not required, we would have been stranded on the hill!


    It has often been argued, particularly by motorcyclists, that drivers cocooned in their "nice, warm cars (VW Type 2s included!?)", lack perception of driving conditions in cold weather and its associated hazards of frost and ice. This apparent isolation, may be partly overcome by fitting a gauge and sender unit, which senses the external ambient air temperature, with a range of -25~40°C. Many such instruments, also incorporate a warning light, which becomes visible, around temperatures at which frost is likely to form. It is also possible to monitor temperatures in the passenger-cabin and elsewhere, if one fits a changeover switch and additional sender units. Fitted into the three-position, accessory instrument pod, of some, or all Mitsubishi Shogun, 4-wheel drive vehicles, is a digital temperature indicator, which simultaneously shows both external ambient temperature and passenger-cabin temperature.


    How many of us have fumbled with a pocket watch (not so common nowadays!) or wrist watch, whilst driving, in order to learn the time? This is both awkward (especially when wearing a jacket or anorak - the normal attire when driving a VW Type 2 in winter) and potentially dangerous. Not only has one's attention been distracted and a hand unnecessarily removed from the steering wheel, but slight twisting of the torso or other upper-body movements, induces one's remaining hand to steer off course. The simple solution, is to fit an easily visible dashboard clock and merely glance at it, when necessary.


    Although fuel gauges provide a general indication of the fuel quantity in one's tank, they are notoriously inaccurate and many give a non-zero reading, when the tank is empty. Owing to the design of float operated, gauge sender units, which utilise the principal of a variable resistor (otherwise known as a rheostat , which may be used in the guise of either a potentiometer or a potential divider), the fuel gauge reading, changes relatively little, as the fuel tank is close to becoming empty. Experience had taught us, that as much as 15 litres (circa 3 gallons) of petrol, sometimes remained in the fuel tank, of our 1973 VW Type 2, when the fuel gauge indicated 'R', for Reserve; dependent upon road gradient and camber.

    Sometimes, the fuel gauge needle seemed to indicate 'R' for ages, but never showed a zero reading, on the occasions when we ran out of petrol. Many modern cars (including my father's former, 1972/73 model, Fiat 124 Special T) have a low fuel-level warning light system, which would also benefit air-cooled VW owners. Although float-operated, fuel-level switches are available, these may not be suitable, for many of the air-cooled VW models, owing to the locations of the fuel tanks. However, it may be possible, to compare the voltage drop (i.e. signal value) across the fuel gauge sender, with a reference value, which corresponds to a known quantity of fuel, remaining in the tank.

    An alternative scheme, which would be unaffected by supply voltage, would involve comparing the ratio (i.e. signal value) of voltage drop across the fuel gauge sender, to the supply voltage, with a reference ratio value. In either case, comparison would be made by some relatively simple electronic circuitry, which would activate a warning light, when the signal value increased or decreased (dependent upon whether the fuel tank was equipped with a dip-pipe or swinging-arm-float, type fuel gauge sender) to the reference value, as the fuel level in the tank decreased.


    Service intervals for the air-cooled VWs and most other cars, are typically specified in terms of mileage or elapsed months, with the caveat that servicing should be more frequent, under certain operating conditions, such as stop-start urban diving or exposure to extremely dusty conditions. Several years ago, in one of their advertising campaigns, BMW actively promoted a feature, whereby the car itself indicated when the next service would be required; the interval having been dependent upon the operating conditions. It is likely, that this facility comprised principally, what is known as an engine hour meter.

    An engine hour meter, which derives its signal from the ignition warning light supply, is rather like an odometer, but instead of counting the total cumulative mileage covered, during the life of the vehicle, it displays the total cumulative time, an engine has run, in minutes and hours, upto a total of 100,000 hours, before the meter resets itself to zero. On plant machinery, such as escavators and dumper trucks, which operate for many hours, but cover few miles, this is a common dashboard instrument, of similar size, price and appearance, to many accessory gauges. Most car or van owners, would probably regard this as a superfluous instrument, but for those whose vehicles are used under mixed driving conditions, some of which may be arduous, an engine hour meter, may be a better guide to optimum service intervals.

    On USA & Canadian (and possibly Swedish too!) specification, 1976~79 VW Type 2s, with Bosch L­Jetronic fuel injection, there were fitted one or more, of three elapsed distance odometer switches & warning lights, associated with the EGR (i.e. exhaust gas recirculation system), CAT (i.e. catalytic convertor) and oxygen sensor, which are included in the appropriate model-year, electrical circuit wiring diagrams, in Chapter 4 – Electrical System, of the Robert Bentley, VW of America workshop manual.

    Judging from the illustrations, depicting Items 13A & 16A~16E, on Page 104, of the official 1968~79 VW Type 2 Replacement Parts Catalogue (shows only the illustrations and Item numbers, of those parts, whose full description and VW part numbers are given on the Microfiche and possibly the recently published CD-ROM), these elapsed distance odometer switches, appear to be activated by either of two system components, interposed between the left-hand, front road wheel and the speedometer; requiring the use of two speedometer drive cables, rather than the usual single cable. I imagine the switches, closed by some mechanism, which illuminate the warning lights, to inform the driver of the need to inspect, service or replace, some system or component.
  17. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation

    Traditionally, the oil change & oil-filter (not applicable to pre-1980, VW 12/13/15/1600 Type 1, 2 & 3) change intervals for VW air-cooled engines, has been specified as 3,000 miles (i.e. 5,000 km) & 6,000 miles (i.e. 10,000 km) respectively, under normal driving conditions. Modern, semi-synthetic and fully-synthetic lubricating oils, which are less volatile and more tolerant of high operating temperatures, require less frequent changing. The literature for Mobil 1 Rally Formula, fully-synthetic oil, specifies an oil change interval of 25,000 miles (i.e. 40,000 km) or 1 year, whichever comes first; maintaining the normal oil-filter change intervals. Given that in 2001, Mobil 1 oil costs more than £30 for a 4 litre can, this is just as well!

    Some oil companies, such as Amsoil in the USA, state that the oil change interval of their fully-synthetic oil, may be further extended beyond 25,000 miles, provided a supplementary, small-particle, bypass filter (filtration of ³1mm particles) is used, in addition to a conventional full-flow filter (filtration of ³20~25mm particles). They justify this, by quoting that dirt particles in the 5~20mm size range (not removed by a conventional, full-flow oil filter), cause upto 60% of all engine wear. To determine precisely when an oil change would be necessary, requires a chemical analysis of an oil sample; a facility offered by Amsoil (priced at £9 in 1992) and possibly other oil companies.

    Periodic chemical analyses of engine-oil samples may be useful, but it requires forethought and record keeping, neither of which are attributes of most drivers. What would be more useful to most drivers, is a device which would illuminate a warning light, when the oil needed changing. Sometime ago, a device of this type, manufactured by Alan Bennett Controls & Technology Ltd., was featured in Industrial Equipment News; a widely circulated engineering-trade magazine. Called the Abtech 'Grid Switch', it continuously monitors engine oil, for the particles of metal, which result from the wear of bearings, pistons & rings, camshaft and valve gear, etc. When the concentration of these particles reaches an unacceptable level, a relay is operated which can be used to activate a warning system.


    As owners of VW Types 2, 3 & 4 will have discovered, these vehicles are equipped with two direction indicator warning lights, both of which flash simultaneously, irrespective of whether the right-hand or left-hand indicator is operating. As I have previously described (see "Reader's Top Tips", VW Motoring, January 1996, p19 & "Reader's Letters", VW Motoring, May 1996, p20, plus "Rewiring Indicator Warning Lamps", Transporter Talk, Issue 30, August 1997, pp25~27 or Technical Information Sheet No. 7), the electrical circuit may be modified, so that the individual warning lights show whether it is the left-hand or right-hand indicators which are operating.


    Normally associated only with off-road, 4-wheel drive vehicles, inclinometers to measure pitch and roll angles, would seldom be considered for most air-cooled VWs. However, the 1968~79 VW Type 2, with its fully independent suspension and low unsprung weight, has long been regarded as the first choice, overland expedition vehicle, for conditions where four-wheel drive was not needed.

    This was certainly true of Theresa & Jonathan Hewat (see "Overland and Beyond", Roger Lascelles, 5th Edition, 1981), who undertook a 3½ year, 90,000 mile World tour, in a 1972 VW 1700 Type 2 motorcaravan; crossing the Equator four times and the International Date Line once. Their journey took them through Europe, the Middle East, Canada, the USA, the length & breadth of both South America and Africa, but omitting Australasia and most of the USSR and South East Asia.

    Arthur Barraclough also travelled extensively (see Simon Holloway, "Van of the Year :- BWR 4H - Arthur Barraclough", Transporter Talk, Issue 18, August 1995, pp 17~20) in his 1970 VW '1600' Type 2 (had a total of four engines; which were upgraded further each time), on and off, over a period of about 25 years, clocking up nearly 220,000 miles, visiting 57 countries, 10 deserts and various mountain ranges (including the Himalayas), all over the World.

    Where one travels over rugged, mountainous terrain, the roads are often unmade, rutted and potholed tracks, intended more for pack animals, than wheeled vehicles, so there is a need to assess the gradient of a hill, which one must climb, descend or traverse. Traversing a hill, is often the most hazardous, because the vehicle may potentially tip over, if the slope (i.e. the roll angle) is too steep. Unmade roads, seldom if ever feature road signs, especially international ones, which might indicate a gradient. As the steepness of a hill increases, so the ability of the tyres (whether conventional, mud & snow or cleated tractor tyres) to provide traction, diminishes.

    Hence, the only convenient way to continuously assess the slope, is by means of dashboard mounted inclinometers. An inclinometer, is also useful when trying to select a level pitch, when camping in a motorcaravan, trailer-caravan or tent. Accessory inclinometers, are available from mail-order companies, such as J.C. Whitney & Company (see Automotive Parts & Accessories Catalogue, Catalogue No. 442D, 1984, pp29~30). Some, or all Mitsubishi Shogun, 4-wheel drive vehicles, have an inclinometer fitted into a three-position, accessory instrument pod, on top of their dashboards. This takes the form of a weighted, graduated sphere, in an alcohol or oil filled enclosure; similar in appearance, to the types of artificial horizon or magnetic direction compass, used in light-aircraft and some motor vehicles.


    With the increasing traffic densities, complexity of road systems and the tendency for travellers to venture further afield, navigation aids to supplement the traditional map and compass, become increasingly important; particularly in those overseas territories, where English is not widely spoken and road direction signs, use non Western European alphabet, such as Greek, Cyrillic, Arabic, Chinese, etc. These days, there are global positioning systems (GPS for short), which are capable of determining one's geographical location (i.e. latitude & longitude, plus altitude in some cases), to an accuracy of ± 10 metres.

    When integrated with a comprehensive digital map, stored on compact disc, some GPS can present a detailed local map, on a screen and issue simulated voice commands about which roads to use and how to proceed at each junction. In recent years, these systems have become more common, as a factory fitted option in luxury cars. Peugeot recently announced, that GPS is now being fitted as standard, to its 406 model. GPS and fully integrated navigation systems, are believed to be already available in the USA, for retrofit, do-it-yourself installation.


    In the interests of safety, many late model, air-cooled VWs were equipped with dual-circuit hydraulic braking systems. When brakes fail completely, it is rather obvious, but when only one of two circuits fail, the signs may be more subtle (I don't know; never having suffered brake failure!) and may not be recognised by all drivers. Some vehicles, equipped with dual circuit brakes, also incorporated a means of warning the driver, if one of the hydraulic circuits fails.

    In many cases, this comprised an alternative pair of hydraulic-pressure operated brake-light switches (three electrical terminals instead of two) and a special warning light module, which like the oil-pressure and ignition warning lights, illuminates when the ignition is switched on and then normally extinguishes once the generator is charging. The wiring diagram for this warning system, is contained in the workshop manuals from Robert Bentley (USA) and Haynes, for the 1972~79 VW 17/18/2000 Type 2, the Haynes manual for the 1968~75 VW Type 4 (i.e. VW 411 & 412), plus possibly some others.

    The 1968~79 VW Type 2 and 1968~75 VW Type 4, standard instrument binnacles, make provision for the special warning light module (VW Part No. 413 919 233B), but if it were unsuitable for one's dashboard, it would be possible to make up a small, remote module (the electronic circuit comprises only a transistor, plus a couple of resistors and diodes), to be used in conjunction with a conventional warning light.
  18. Dingostrategy

    Dingostrategy Active Member

    SW Vic ++
    Hay Nige,

    This is classic. But uploading a PDF might be easier? These threads are a bugger to print.

    Text only should attach without too much hassle?
  19. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    If paying due care and attention to road and traffic conditions, it is usually possible to reduce speed when necessary, merely by easing off the throttle, without applying the brakes. However, all too many drivers are inattentive and follow too close, for the prevailing conditions; creating the need to somehow alert them to one's reduction in speed. The obvious way to do this, is by activating the normal brake lights, but it is not always easy to positively achieve this, without simultaneously applying the brakes. One simple upgrade, involves merely connecting a dashboard warning light, in parallel with the normal brake lights, so that one knows when the brake lights have illuminated.

    A further refinement, which eliminates the need to use the brake pedal, entails fitting a momentary-on/off switch (circuit is closed, only whilst one maintains pressure on the push-button or lever), connected in parallel with the normal brake-light switches. This may be located, either on the floor (akin to the old style headlamp dip switches), dashboard or steering column. If a relay is incorporated into the brake-light circuit, additional brake lights (e.g. high-level and/or trailer brake lights) may be operated, without overloading either the supplementary momentary-on/off switch or the normal hydraulic pressure-operated, brake-light switches.


    Although a safety critical component for all vehicles, few drivers regularly check their tyre pressures and of those who do, most probably check them less frequently than once per week. Police patrol drivers, are obliged to check their tyres, each morning! Tyre pressures vary naturally, as a consequence of changing climatic conditions (pressure increases with ambient temperature and solar intensity) and the pressures of 'cold tyres' should be progressively adjusted to compensate. Tyre life will be noticeably reduced, if the tyres are significantly under-inflated or over-inflated.

    Under-inflated tyres also result in excessively heavy steering and are liable to overheat, owing to excessive flexing of the sidewalls and in extreme cases, the tyre can fail catastrophically. Although increased tyre pressures makes steering more positive, it becomes increasingly light, such that the steering loses 'feel' and sensitivity to slippery conditions. It might also cause the vehicle to feel skittish on bumpy roads, as a result of having increased the effective stiffness of the suspension; a phenomenon I observed, after experimentally increasing the front & rear tyre pressures of my Triumph Toledo 1300, by only 2 PSI, from 22 & 26 PSI, to 24 & 28 PSI respectively, as recommended for the Triumph Dolomite 1300 (a closely related model).

    On vehicles with sensitive steering (such as my Triumph Toledo), a disparity of only 2 PSI between the front tyres, can result in noticeable steering wander (i.e. if under non-windy conditions, on a level road with no camber, the steering wheel is released, the vehicle will drift to one side), which becomes more severe under braking. Differences in pressure between front and rear tyres, is one factor which influences oversteering and understeering characteristics; an effect commonly utilised on rear-engined vehicles, of which the VWs with air-cooled engines, are a well known example.

    These days, instrumentation developed within Dunlop's Advanced Tyre Department (see P. N. Griffiths, "Never tyre of keeping the pressure on", Daily Mail, Saturday, 23rd March 2002), is available to constantly monitor the tyre pressures, by means of the wheel's changing vibration characteristics, which increases as the tyre deflates. This system, is now used by BMW and other car manufacturers. Another possible system would involve a pressure sensor on the wheel rim, transmitting a signal to a receiver on the car body. Whether it would be practical to retro-fit such systems to existing vehicles, I don't know!

    One example of a less sophisticated device, is a tyre valve cap, available from Monitortire Inc., in California, USA or Monitortyre Ltd., in Surrey, England, which changes colour, as the tyre pressure changes. At normal inflation pressure (with a cold tyre, at ambient temperature), the valve cap is green. When the tyre pressure falls more than 4 PSI below normal or increases by more than 10 PSI above normal, the valve cap changes colour, to red and yellow respectively. Valve caps with different normal-pressure ratings are available.

    A similar product, called Pressure Guard (believed to be made by Visscher-Caravelle UK Ltd.), is available from Auto­Unique Ltd., in Pangbourne, Great Britain, priced at £12·50 for a set of four. This product is automatically self-calibrating, resetting itself to the air pressure in the tyre, at the time it is screwed onto the Schräder valve. As the pressure drops below the set value, a green indicator receeds, revealing a red core. Pressure Guard is said to indicate when the air pressure has fallen by more than 2 PSI, below the calibrated pressure. During the late-1960s or early-1970s, I used another simpler type of universal valve cap, which could be manually adjusted to indicate the tyre's normal pressure, but it was susceptible to tampering, by unscrupulous persons.


    When making provision for trailer towing, fitting electrical accessories or upgrading the vehicle's instrumentation, it is often necessary to make provision for several warning lights. To fit a large number of separate warning lights is often impractical, but this may almost invariably be overcome, by fitting a single warning light cluster, such as the circular one made by Lucas, which was a standard fitment on several BLMC Triumph cars, such as the 1300, 1500, 2000, 2500, Dolomite and Stag. If not available second-hand from car breakers' yards, these warning light clusters are available new, priced at about £12, from Triumph specialists, such as Rimmer Brothers, in Lincolnshire. However, it is probable the matching multi-pin connector block, will only be available from salvaged vehicles.

    The Lucas, 60mm diameter cluster, which may be readily customised (see Nigel Skeet, Transporter Talk, Issue 33, February 1998, p21) for accessory use, comprises eight equal segments with interchangeable plastic filters, of five different colours. It is possible to substitute one's own warning symbols and to supplement the standard range of filter colours, using self-coloured acrylic sheet (e.g. ICI Perspex). I now have eight different colours available to me, which are:- red, orange, yellow, light-green, dark-green, light-blue, dark-blue and magenta. Since my aforementioned article was published, I have also devised an alternative way, of producing a transparent mask with customised symbols, using a computer graphics package, such as Adobe Illustrator.

    As mentioned earlier, conventional warning lights may go unnoticed, unless observed at the moment of illumination. It would be distracting to have multiple flashing warning lights, but one or two buzzers (VW part No. 111 951 307B – plugs into an accessory relay, mounting cum connector block) and/or flashing lights, such as the flashing coloured LEDs, available from car accessory shops, could be linked to the conventional warning lights, via a bank of blocking diodes.
  20. Nigel

    Nigel Member

    Canvey Island, Essex, UK
    Retro-fitting supplementary instrumentation


    At this juncture, you are probably wondering how much of this highly desirable instrumentation, it is possible to accommodate in your air-cooled VW; either within, above or below the dashboard, plus special consoles above the gear selector tunnel (not VW Type 2) or at roof level. At present (i.e. early-2003), my family's 1973 VW Type 2 is equipped with a total of nine 52mm, accessory gauges, for oil pressure & temperature, cylinder-head temperature (with changeover switch for two sensors), inlet-manifold vacuum and ambient-air temperature (with integral frost warning lamp), plus rev counter, voltmeter (with changeover switch for main fusebox supply and regulated alternator voltage), internal-shunt ammeter (to monitor battery charging and discharging rates) and quartz clock. I hope to one day acquire a remote-shunt ammeter, which is better suited to rear-engined vehicles.

    A brake circuit failure warning light unit and two conventional, supplementaty warning lights, fit into the 430mm wide, standard instrument binnacle, together with a Lucas, 60mm, 8-segment warning light cluster. In addition to the standard warning light functions (i.e. left & right turn-signals, main beam, parking lights, oil-pressure & generator), there is also provision for dipped beam, trailer turn signals & brake light illumination. There are dashboard switches, with integral warning lights, for front & rear fog lamps, auxiliary driving lamps, auxiliary 'reversing' lamps, roof-mounted 'work' lamps and heated rear window. If and when the necessary switches, transducers and control circuitry, have been acquired and fitted, there will be warning lights and/or buzzers, for engine detonation, engine-oil & cylinder-head overheating, plus unlatched doors, hatches & elevating roof.

    Six gauges, are presently mounted in a single supplementary panel (in two rows of three), together with two changeover switches, in the centre of the dashboard, where a radio would normally be fitted. The three other gauges (including the quartz clock) are mounted in a bracket, on top of the dashboard. As an alternative to the bracket, I could have used a single, multi-aperture instrument pod, such as those made by Sedan (available by mail-order from Europa Specialist Spares, for either one, two, three or four 52mm gauges, side-by-side). In my pending-projects box, are another Lucas, 60mm warning light cluster and accessory VDO 'Cockpit', 80mm accessory speedometer & rev counter, plus 52mm gauges for fuel-level and 40~120°C 'water temperature'.


    These, together with my existing supplementary gauges will enable me to create a matching, co-ordinated system; making redundant, all the standard instruments and their associated binnacle. However, before I can do that, it will be necessary to fabricate a 650mm wide, custom instrument binnacle (either one or two piece - divided at the heating & ventilation control levers), if and when I find a way to make it! This would replace both the 430mm wide standard binnacle and supplementary six-gauge panel, which in most cases, should obviate the need for the gauge bracket or pod, on top of the dashboard. As well as being a neater installation, the custom binnacle should enable me to optimise the instrumentation ergonomics.

    If at some stage I decide to also fit an altimeter and inclinometer (probably salvaged from a Mitsubushi Shogun, 4-wheel drive vehicle, in a breaker's yard), then it will be necessary to have an accessory instrument pod, on top of the dashboard. Recalling the position of the steering wheel rim, a 650mm wide binnacle, will accommodate unobstructed, two 80mm gauges, two 60mm warning light clusters and nine 52mm gauges, plus various small switches and conventional accessory warning lights. If one opts for only a single 80mm gauge and two 60mm warning light clusters, then the binnacle could accommodate twelve 52mm gauges, but two of these, would be at least partially obscured, by the steering wheel rim.


    In the past, revising the electrical wiring, to reposition existing switches or incorporate additional instrumentation and switches, had proven both difficult and tedious, so I fabricated a replacement modular wiring loom, using the existing cable, plus additional cable and multi-way connector blocks, of appropriate current rating, salvaged from various models of scrapped cars. The left & right-hand sides of the dashboard and instrument panels, form separate modules, which may be disconnected from the main loom, simply by unplugging some of the in-line, multi-way connector blocks.

    As well as making any later modification much easier, this modular system enables the instrument panels, or even the complete dashboard, to be removed and refitted very quickly, without needing to label any wires, providing easy access for maintenance (e.g. replacing instrument-illumination & warning-light bulbs, windscreen wiper motor, etc.) or repair.

    Connection to many of my 52mm VDO 'Cockpit' accessory gauges (water & oil temperature, oil pressure, fuel level and volts) is made using matching 3-way connector blocks (VW-Audi part No. 321 971 970 or VDO part No. 89-098-008), salvaged from various water-cooled VWs and Audis. Connection to either of two VDO oil-temperature dipstick senders (VDO Part No. X10·323·003·001 and X10·323·003·002), may be made using a standard 2-way connector block (VW-Audi Part No. 321 941 600), normally associated with headlamp-unit incorporated parking lights or hydraulic-brake master cylinder switches.

    Although the cylinder-head temperature gauge kit, is provided with standard copper cables, for connecting the thermocouple sender (strictly speaking, it's called a thermojunction!) to the gauge, these are not ideally suited to this purpose. By its nature, the thermocouple generates a small EMF, of probably less than 40 µV/ºC; corresponding to an EMF of only 0·012 V, at a cylinder-head temperature gauge's maximum reading of 300ºC. Given that the gauge is a high-impedance voltmeter of several thousand ohms, the resulting current is negligible, requiring only thin wires.

    However, being an exceedingly small voltage signal, it is very prone to induced electromagnetic and electrostatic interference (i.e. electrical noise), from the electrical system, the engine's ignition system and other sources. To minimise the effects of such interference, one is advised (see T292 Instrumentation, Open University course reader) to use screened, twisted-pairs cable (preferably screened by aluminium foil or aluminium foil & tinned-copper braid together), isolated as far as possible from the main wiring loom and crossing it wherever necessary, at right angles. To avoid the creation of an earth loop, whereby a potential difference exists between the end of the cable screen, the screening copper braid should be connected to earth (i.e. ground), at one end only.

    Having two thermocouple sensors (one for each cylinder head), on my 1973 VW Type 2 engine, I used an approximately 7 metre length of screened, double twisted-pairs cable (screened by aluminium foil & tinned-copper braid together), connected to the gauge and sensors at either end, by means of short lengths of conventional sleeved cable, plus male & female, 5-pin DIN, audio cable connectors. The screened cable and 5-pin DIN connectors, should be readily obtainable, from most electronics or computer suppliers, such as RS Components, Farnell, Maplin Electronics, Tandy and Inmac.

    Vacuum connection between the vacuum gauge and the engine inlet manifold, is achieved using short lengths of flexible tubing, in conjunction with, a semi-rigid, small-bore nylon tube (purchased from a local, industrial, hose & tube wholesaler), running from inside the rear engine compartment to the back of the dashboard in the cab. The small-bore nylon tube, is routed within the main, front to rear, wiring loom sleeving and conduit.
    Last edited: May 29, 2010

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