Kai, I think that you might be onto something. I think that the sender is expecting a different range than the gauge hence the reason it's showing a low reading.
Kai, after looking at some stuff at DOTVW, I think that the sender and the gauge aren't matched. I noticed on the JK site that there are two types of oil temp sensors, dipstick like the one I have and the sump one (although it doesn't look like there is a sump model for the 2l motors). What are people's preference for either of these options for a 2l motor ?
I have the dipstick sender - there's lots of theories about it not being in the right spot to get the correct temp, but in my opinion, it's not really about what your actual temp is - it's about showing what's normal and what's not. As long as it shows you when your normal engine temp has gone up 20-30 degrees for some reason, then you at least know to pull over and let your engine cool down and find out why it's getting hot. Trust me, I have some experience with engine temps!
dipstick is fine but i like using this inspection plate replacement from the UK. http://www.thesamba.com/vw/classifieds/detail.php?id=978324
Kai, how does this one differ from the one at JK? The samba one talks about replacing the inspection plate. Is that what the JK one does too?
You need the sump sender inside the billet inspection plate replacement. You can not use the normal sump plug sender in a type 4 case (if it hasn't been stripped before) as it should be m12. the dipstick sender replaces your original dipstick but you need to keep your original dipstick for level checking. Alternatively you can drill a 14mm hole in your current inspection hatch and put a nut on the otherside and seal it with some JB Weld. that has been done before on the samba. I like the billet replacement because it protects the sender
Or tap the case at #1 and run a 28NPT model. Both sender and wires are high up away from snags and dags. The VDO 28NPT sender is matched to the VDO 150 degree gauge.
tapping the case is beyond most hobbyists, this solution is just two allen key screws and a sender. all gauges should be used a a guide to look for abnormalities, ie if youre driving at 60kmh and your oil temp is normally 80-100 degrees and all of a sudden it is 130 degrees then there may be something wrong.
T'was just another option Kai, that when all costs are included (exchange rates, freight, etc) comes pretty close to 1 hour of pro shop time - which is what it should take to tap the case. Here's another one (the real one) for the Porsche 911 914. Which ever way ones goes, gauges is good. http://www.autoatlanta.com/Porsche-Oil-Sump-Cover-taco-Plate-Parts-PN-G039101267.html
maintaining a kombi is against most hobbyists! - If they can use the allen keys and wiring and sort a gauge out, chances are they can drive a drill and tap....