Thermostat opening temperature

[Froggy_130]

Hi Guys,

Wondered if anyone knows off top of their head what the opening temperature should be for the thermostat in my car? Its a 2001 Passat TDi 130 PD, engine code AVF.

Vagcom shows the coolant temperature struggles to get over about 78 degrees after 30 mins of driving. I've tried two new coolant temp sensors which gave the same result so I'm fairly sure they are ok.

Have also tried blocking off half the radiator with cardboard in the front grille, didn't make a difference.

The car has had a new thermostat but I think it must be faulty/incorrectly specced as I guess it must be opening too early.

Anything else that could cause this? Electric fan isn't on permanently and I'm able to turn the viscous fan by hand (carries on about 1/4 of a turn when I spin it pretty hard) when cold so I think that is ok. I've checked the coolant concentration which is good for -20 degrees c.

Ta in advance!

Cheers,
Dave.

[martin1810]

Some people have found vag-com temp reading to be plus or minus 20 degrees when the guage is reading 90 degrees. The only way to know exactly what your thermostat is doing is to take it out and test it. Your reading of 78 degrees would be "in spec" on a lot of cars.

[Froggy_130]

Thanks for the input Martin. So even though vag-com shows 78 degrees the sensor may actually be reading 90 and the ecu seeing 90?

Would it be worth checking the coolant temperature in the expansion tank with an infrared thermometer? If that reads 78 then I guess that points to the thermostat?

My mechanic is replacing the thermostat again on Friday so I'll ask him to test the new one before it goes in

[martin1810]

If the sensors are good then the vag-com read is probably correct. It seems to be the temp guages that vary. It is as if the guage will read 90 degrees as long as the input is within a certain range, rather than actually being 90 degrees. The vag-com figures need to be as near to spec as possible because the ecu is using those figures to adjust fueling. An IR thermometer is ideal test but even that needs to be checked carefully. I have seen them read wrong temperatures before now. Check that the one being used has been calibrated.

[snapdragon]

I think they are all 87˚C on our cars, mine is and a quick google seems to confirm it.
http://www.google.co.uk/search?clien...#730;&ie=UTF-8

[jammy86]

I would have though its about 75~80 degress at the most.

The guages aren't directly controlled from the sensor I dont THINK. I was doing some testing on a Defender a while back and the guage on the dash sits a 90 all day long. The engine temperature (measured from the same sensor as the uage runs off) was as high as 110 on full load but still the guage was 90.

Its just there so you think you know something, but really I'd be surprised if the guage was remotely accurite.

If VAGcom says its 78deg, its 78deg. Thats what the ECU thinks the engine is at, even though the guage might tell you 90.

JAmes.

[Crasher]

Opening commences approx. 85 °C, ends approx. 105 °C. Opening lift min. 7 mm.

[Froggy_130]

Cheers all - just the info I was after. I'll ask my mechanic to test the new thermostat to make sure it is working to spec.

Thanks again!

[Froggy_130]

Quick update - bought and installed new thermostat (tested first and starts to open around 85 degrees, spec is 87) and vag com now reading pretty well dead on 90 degrees when up to temp.

MPG has improved slightly - up to about 45 to the gallon now which is better than it has been but still not as good as it used to be! Next job is turbo clean to try to sort my overboost problem!!

Cheers for your help guys