I own an Audi TT 1.8, 2001. Temperature gauge stops at middle, but after the car is warm it fluctuates between the middle and the first tick. Specifically, when I stop at a red light for a period of time. The temp. returns to middle after acelleration. I replaced the temp. sensor and the Expansion Tank Lower hose, which had a pinhole leak. But this does not fix the problem. Any ideas appreciated.

 

There are four possible problems; 1-temp gauge is falsely reading, 2-thermostat, 3-waterpump, 4-radiator fan/fan control module. When it starts rising throw the A/C on, that should automatically throw the fans on and if it drops in temp then there is a fan issue.

 

To quote:

1. "One other thing water pump prob, (lack of impellor blades) usually shows up at speed rather than idleing."

This does not happen, and also I have not detected any leaks or noises.

2. "The fact that engine cools dramatically when back up to speed would probably mean thermostat is opening as it should (normally when faulty these fail to close causing low temp). "

The engine temp. cools when up to speed., and does not rise past midpoint. Nor does it sit at low temp.

Lastly, my temperature gauge reads the same whether the a/c is on or off.

I talked to the stealership today. He said I should not worry if the temperature gauge dances around between middle and first notch when idling in traffic.., as long as it is coming back down to the middle. Perhaps I am worrying about nothing?

All opinions welcome!

 

Just wanted to list the "possible issues", I know there is a trick you can do with your heat controls (is that right someone?) and it can actually display the engine temp on that as a second gauge to see what its actually at to diagnose the gauge? My gauge does the same thing but when I kick the a/c is will bring it down before I even take off from idle leaving me at the electric fan, I guess its a TT thing because my b5 a4 never had this issue and when you google Audi TT cluster issue its never ending

 

Correct me if I'm wrong, guys. To get a digital coolant temp reading, on the climate control panel, hold down at the same time the 'recirculate' button and the 'up' arrow (it's the one on the upper right corner of the climate control panel). Code '1' will come up on the display. This may take several tries. When it does, turn the temperature setting **** to the right until code '49' is displayed. This is the coolant temperature reading. If it goes over 100 celcius, you'll notice the temp gauge on the cluster will go past the middle notch. Whew! I hope that was clear.

 

By the way, I always run the a/c when I get in stop and go traffic to keep the fans running.

 

Thanks Dozanti for outlining all the possibilities:-) This is my first time to explore how my car really works, and I have learned much from you (and others) about my cooling system already. Seriously, I didn't even know what a water pump, or thermostat really did for my car before now!!

Fireman 9585, I have a question about your suggestion. I tried to get a digital coolant temp reading on the climate control panel by holding down at the same time as the 'recirculate' button and the 'up' arrow.

It worked as you said. But I am a bit confused. Do I stop at 49? and then wait for it to do something? If I continue to turn the temp. setting ****, it will continue to go up., but stops at 80. Even if the temp. gauge needle is dancing between 1/2 way mark and the first tick -it still stops at 80. Little confused on how this gives me a reading.. I'm assuming if the car gets hot, then the gauge will keep going up past 80?

I think I would be able to relax more if I knew for sure whether my car is overheating or not.

Lastly, I wonder if I need a coolant flush?

Thank you!

 

Sorry. I knew there was another step. When you select the code, as in '49' for instance, you then press the recirculate button again, this time by itself, to get a temperature reading. It will read in degrees Celcius. Hope that is clear.

 

I'm having the same issue! I changed the coolant and did a flush, I changed the green temp sender,I recently maybe 10,000 miles or so the water pump timing belt etc, changed the larger fan and the fan switch, both fans kick on, same when stopped at a red light gauge goes 1/4 past half. no overheating, just worried it might be. So I was told we have a circulation pump relay under the drivers dash #J151, now stealership I'm sure wants and arm and a leg, might this be the problem with the TT Temp Gauge Issue?
And can this relay only be purchased at the stealership?

 

Thanks fireman. I tried the method you suggested to test the coolant. It is running between 27 and 28 C.., even when the temp gauge is past the middle (sitting at the first tick after the middle). So I'm guessing the car is not actually running hot. It really helps to know my car is not really running hot!

One more question about the test method.., do I have to leave it on code 49, and then push the recirculate button, or can I leave it on any number?

Coachvtt: thanks for sharing! -do you know what exactly the circulation pump relay under the drivers dash #J151 does?