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thermostat repair

Discussion in 'Engine & Transmission' started by robmich, Apr 2, 2020.

  1. robmich

    robmich Active Member

    Messages:
    564
    Location:
    buff point
    just wondering if anyone has successfully repair thermostat bellows, if so how did you do it
    Rob
     
  2. Barry

    Barry Well-Known Member

    Messages:
    5,995
    Location:
    Abbotsford NSW
    tintop likes this.
  3. rstucke

    rstucke Well-Known Member

    Messages:
    1,902
    Location:
    Wamberal NSW AUS
    not necessarily
    The fluid is isopropyl alcohol
    There's a how to on the samba
    I'm having a go when I get around to it as I've got a failed unit
     
    David H likes this.
  4. Buggergary

    Buggergary Well-Known Member

    Messages:
    90
    Location:
    Smithton Tasmania
    While we are on the subject of the thermostat can anyone tell me how you set them up? I removed the cable to take off the tinware and paint it.
    When I put it back on I just closed the flaps and lulled the cable tight then locked it off.
    A few days later I happened to move the flap bar and moved and the cable was lose and the flaps were only half on.
    I held them closed again and pulled the cable taught again but I was wondering it there is a correct way to set it up?
     
  5. David H

    David H Well-Known Member

    Messages:
    6,646
    Location:
    newcastle
    [QUOTE="
    When I put it back on I just closed the flaps and lulled the cable tight then locked it off.
    A few days later I happened to move the flap bar and moved and the cable was lose and the flaps were only half on.
    I held them closed again and pulled the cable taught again but I was wondering it there is a correct way to set it up?[/QUOTE]
    Temperature? Expansion/contraction?
    Cheers
     
  6. Buggergary

    Buggergary Well-Known Member

    Messages:
    90
    Location:
    Smithton Tasmania
    It's only been about 15 deg round here for the last week or so since I hooked it back up so didn't think temp would affect it.
    I had the cable disconnected for a month or so. So I was thinking it may have shrunk with no tension on it then once I hooked it back up the tension might have moved the bellows a bit now the weight was on it all the time. I'm hoping that now it should be settled back to normal and it won't go slack again.
    I don't want to damage the bellows and they look expensive :( so I thought if there was a proper set up for them I should be doing it.
     
  7. robmich

    robmich Active Member

    Messages:
    564
    Location:
    buff point
    iv got 2 failed units I was thinking of using something like that goop they seal fuel tanks with that you slosh around inside ,should be resistant to alcohol im thinking,just don't know if it would be flexible enough
    Rob
     
  8. David H

    David H Well-Known Member

    Messages:
    6,646
    Location:
    newcastle
    So hand sanitizer is the contents @rstucke ?
    Cheers
     
  9. rstucke

    rstucke Well-Known Member

    Messages:
    1,902
    Location:
    Wamberal NSW AUS
    Buggergary likes this.
  10. Doob

    Doob Member

    Messages:
    49
    Location:
    Perth
    Has anyone here ever tried to repair a bellows type thermostat with any success? - Using this methodology given by Richard Atwell or by other means?
    [i.e. link provided by rstucke above ....https://ratwell.com/technical/Thermostats.html ]
    Also see this Samba link for a variation of this repair method ..with some good photos!
    https://www.thesamba.com/vw/forum/viewtopic.php?t=587449
    Has anyone tried the Awesome Powdercoat thermostats out of USA ?
    Anyone aware of any other thermostat replacement options?
     
  11. BrissyGeorge

    BrissyGeorge Active Member

    Messages:
    314
    Location:
    Brisbane
    So how do you know whether the thermostat is working or not - what check can you make (with the thermostat still in the car preferably?
     
  12. Doob

    Doob Member

    Messages:
    49
    Location:
    Perth
    Re, checking the thermostat is working....
    With the thermostat in place you would need to watch for movement in the cooling air flap linkages, as the engine heats up from cold to a temperature above the thermostat rating - e.g. above 65 -70 C for my Type 1. This may not be easy to do. However several internet sites discuss removing the bellows thermostat, and putting it in a water bath. Progressively heating the water bath and watching for expansion of the bellows. Fully contracted when cold (about 35mm) to fully extended when hot, about 46 mm, according to the Bentley workshop manual.

    My understanding is that this bellows type thermostat chamber should contain a small amount of liquid with a specific boiling point, and very little air.

    When cold the bellows is fully compressed by the external atmospheric air pressure. In this cold compressed state I think the bellows should be about 35 mm tall.

    When the liquid in the bellows heats up and reaches boiling point, the liquid vaporises and increases the internal pressure very quickly. The bellows expands with the increase in pressure, from a height of approximately 35mm to 46mm over a very small temperature increase - pushing up the connecting rod and opening the cooling air flaps. I assume the internal liquid added at manufacture had a boiling point in the range of 65 – 70 C. I guess it was some alcohol mixture. The repair blogs talk about using isopropyl alcohol, as it is easy to get ....usually! This has a boiling point of 82 C. Not sure what liquid was originally used.

    Then when the bellows cools down, the internal vapour condenses, reducing the internal pressure back to near vacuum conditions, and the external air pressure compresses the bellows back to approximately 35mm.

    If the bellows leaks, air will enter the chamber (and the internal liquid will escape). This will equalise internal & external pressure, and allow the bellows to expand to almost it’s full height. [i.e. it fails to a ‘safe’ state – similar to the hot state - with the air cooling flaps open).

    My thermostat was 41 mm tall at room temperature. I put it in the fridge for a while (4 C) - then into a sealed plastic bag and placed it in a water bath. Progressively heating the water & taking measurements of the bellows up to a temp of 90 C. Unfortunately my thermostat remained pretty much at 41 mm at all temperatures (4 to 90 C) - Thus I can assume it no longer works & probably has a leak.

    Hence I am now looking for repair or replacement options.
     
    David H likes this.

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