02 B6 1.8 T: fans run within 30 seconds of cold startup. Temp guage pegged mostly at C, will eventually rise to 1/3rd. None or very little heat once engine is warm. I replaced the temp sensor at the firewall, no change. Was going to replace the thermostate next, however, I suspect the problem is electical since the cooling fans are sensing a hot engine. Is there another temp sensor or is it likely the sensors in the thermostate housing. Note that this A4 has the non-servicable thermostate housing...Any suggestions?

 

If I'm not mistaken, the fans are supposed to run on a cold start-up (I may be wrong tho.) as far as no heat, have you checked your coolant flange? (its right next to the temp sensor you replaced.) Also, is your a/c giving you any issues because that can sometimes cause your fans to run more than they need to.

 

If you're getting minimal heat then it is probably your thermostat (coolant not circulating properly because it's not opening all the way). I could be wrong but I know there's a DIY out there and you don't have to remove the whole front to do it. Yes, it's the entire housing and not just the thermostat you would have to replace.

 

There is another temp sensor, dont know if it controls the fans or not. It is on the drivers side bottom of the radiator, in the hose.

I had to change my thermostat a few months ago and it wasnt that hard. Got the part from aboveallmotorwerks.com and saved a bunch of money. You have to pull the alternator and throttle body to do it.