2003 a4 1.8tqm. Just had thermostat done a little over a week ago. Last night I was parked at dairy queen and my coolant starting boiling over. Now of course I'm low on coolant and my temp gauge keeps going up and down.. any help please. The last couple of posts I got nothing! Come on guys help an Audi brother out ha

 

Is the coolant full?
Does it leak out when you pour in new coolant/water?
Did you bleed the cooling system?
Why was the thermostat replaced in the first place?

 

Another thing I got from reading your post is, you said, "gauge goes up and down." It is very possible the thermostat you had changed is bad. I always take them out of the box brand new and put them in hot water on the stove to test them before putting them in. It could have been failing and then finally failed shut. Also what m5s5 had asked, did you bleed the system of air when you changed the tstat? It's very possible the system got air locked and caused your problems.

 

It doesn't leak out, it was a little low. The thermostat housing blew out on me that's why I replaced it. It was bled out when installed.

 

the thermostat was done professionally, so i hope they checked it. but my heat is good when the car is cold or warm. This morning on my way to work it didnt overheat and last night after it cooled down it didnt overheat again. Could this be a water pump? i dont think so only because if it was a water pump then it would just overheat immediately right?

 

okay so i have a little bit more information. the car was completely cooled down just now. I went outside and started it with the heat on full blast and the coolant cap off to see if there was air in the system. It ran for about 10-15 minutes got all the way up to temp and a couple of different outcomes, one was the coolant in the tank stayed at the exact same level, another was that when i squeezed the upper radiator hose there was no pressure and no fluid running through it. Also once it got up to temp i turned the a/c on full blast to see if it would over heat and the temp gauge instantly dropped all the way below a quarter!! Please some one help me out on this i know very little when it comes to cooling systems!

 

I'm wondering if your system has air in it. The overflow tank can be full but you could still have air in the system. If you take the cover off of the engine, there is a black metal cooling pipe, with a bleeder screw on top. With the engine warm and the car running, the coolant in the expansion tank should stay at the same level except the small hose that runs to the top of it should be flowing coolant out of it into the tank. If you dont have that flow, I would have to think you still have air in the system. Get the car warm with the cap off, on an incline and have someone slowly rev the engine to around 2k rpm while you massage the cooling hoses (burping the system).

 

i did that and nothing has changed! anything else i should check? I think im gonna give in and bring it to my mechanic tomorrow

 

I'm wondering if you got a faulty tstat, with a combo of a bad temp sensor ($35). Okay lets start from the beginning, this is really bothering me haha.
From beginning: Why did you have the tstat replace, was it for preventative maint.?
The car was fine for a week after the change, and all of a sudden it boiled coolant out.
You let it cool and it was fine for a few days, now with good heat if the a/c is turned on it over heats? Have you confirmed your fans are kicking on? If they are, this could be a coolant sensor. Try turning the heat on with the "econ" off, this should kick the fans on, see if it warms up then.

 

Oh is it bothering you? ha I replaced the tstat because the housing blew. Ever since it overheated i cant get it to overheat again, with the a/c on or not. But the fans turn on when my heat is on. is there anyway to see if the tstat is bad or not?