mrtiger

My wife's 2001 TT roadster is overheating. Shortly after starting the car it pegs the needle to hot and the warning light comes on.

I replaced the water pump, thermostat, coolant temp sensor, coolant reservoir, fan control, backflushed the cooling system and filled it with G12 and distilled water.

The system has been burped numerous times and the coolant level is constant.

There is no steam or sweet smell from the exhaust, no coolant in the oil or oil in the coolant.

I'm at stumped, does anyone have any ideas???

03_AR_CO

You've replaced just about everything, the TT coolant system is not all that complex. If it were just the gauge pegging hot, I would suggest the instrument cluster, specifically the gauge is in need of rebuilding. Combined with the warning light makes it unclear to me. Still may be the gauge. I suggest connecting your VCDS cable to the car and look at the engine management measuring blocks as well as any fault codes a full scan might provide. Could be as simple as a faulty reading on the gauge, the scan should tell you.

mrtiger

No codes, the temp goes up to 124C

03_AR_CO

So you are about 40C above normal. What manufacturer thermostat did you use, Genuine Audi? Also do both fans run when you are getting this reading?

mrtiger

Audi thermostat, fans run.

I believe it may be a head gasket.

03_AR_CO

Is your coolant boiling over, I have had head gasket failures before, never on an Audi. Usually can smell exhaust gasses in the coolant reservoir, if really bad traces of oil in the coolant, and traces of coolant (brown sludge) in the oil. If this is the case I am sorry to hear it, but should not be too terrible replacing, especially if not a daily driver. I'll look for your progress.

mrtiger

No coolant boiling, no exhaust gas in reservoir, no oil in coolant. Ill keep you posted with the outcome if I get this figured out.

De-audi

I had this problem on my TT Coupe for at least 2 years. Erratic temperature, moving from 90 deg to about 125 deg and back at times. I replaced all the cooling system components less the radiator. But it did not solved the problem.
One day, the air-cond blower fan motor gave way. Had it changed and refilled the air-cond system with gas and vacuumed. The temperature has been constant at 90 deg ever since.
Recently, my TT 2001 Roadster registered an erratic temperature, as above. The air-cond wasn't cold. The radiator fan cut in and cut out frequently. Refilled the gas and the temperature is normal at 90 deg.
Since you had worked on all possibilities and there was no leakages, you may consider this option.

Mister Bally

If the needle pegs and warning light comes on immediately when you start a cold engine; you do not have a true overheat problem. You have a malfunction of the warning system. Time to troubleshoot using the repair manual (buy from Bentley Publishers if you don't have) and use standard Automotive Electrical system troubleshooting techniques along with a good multimeter to diagnose and repair.