I am looking for some advice. I have not worked on many Audis in my time but have worked on many cars. My friend has a 00 Audi A4 turbo. It was getting very little heat.. So I put a Thermostat in it. Now it will get heat going down the road but at idle the heater blows luke warm to cool within 1 min. So at this point I figured I got a bad T-stat and replaced it again. I still had the same issues. I have a vaccume fill system and was able to pull and hold 25lbs of vac and it filled the system. Now, other symptoms.. in a right hand turn, the temp gage drops to cold, and never goes above half way. The lower radiator hose never gets warm to the touch but the upper runs about 195.. The hoses going to the heater core are both above 150, The lower rad hose is 65 degrees. There was alot of sludge in the cooling system and I ran a flush thru it 3 times until it was coming out clean. I did refill with a 60% mix of Audi g12 A/F. I am wondering if there are any bleed valves on the turbo or pipes that I have missed. This really acts like an air bound issue, bbut I dont know any better way of bleeding the system. If there is a special procedure I would appreciate any help. Thanks John

 

You may want to try the coolant temp sensor. It's located between the engine and the firewall. It's a cheap part and much easier than the thermostat.

 

I did not see a sensor between the engine and firewall, but there was one in the lower rad hose, right by the radiator.
Would the sensor make any difference even if that lower hose is not warming up? Does the heater valve not open if the sensor is reading cold? thanks

 

I honestly know very little regarding the cooling system. What I do know is that it's goofy as all hell and the part is cheap to replace.