My 2001 TT just started over heating or at least the instruments are reporting an over heating issue. About 6 months ago I noticed that the temperature gauge started reading one segment higher than it normally ran; it had always pointed at the 12 o'clock position and then started to go to about 1 o'clock. Recently I have seen it climb past the 1 o'clock segment and into the next segment over (see picture). If I turn on the cabin heat and run the fan at full I can drop it back to the 1 o'clock position. If I don't turn the heat and fans on high I get the warning light and audible alarm. My fluid is topped up and if I run the climate control diagnosis "code 51 - Engine Coolant Temperature (ECT) in deg C" it never reads above 90C although I would expect this to fluctuate with the fluid temperature.

From startup my engine temperatures reported this using code 51:

Gauge Position ...... Temperature Reported
Start ..... 35C
1st Segment ..... 57C
2nd Segment ..... 63C
3rd Segment ..... 77C thru 88C
4th Segment ..... 90C

When the needle was sitting at the 4th segment and I checked to see if the radiator fans were running, neither one was operating.

I'm thinking a complete flush, new thermostat, new water pump and testing the fan thermostat/control modules.

Any other advice and any idea why the temperature reading for the "code 51" output wouldn't fluctuate?


EDIT: Note that code 51 is incorrect for an AudiTT and is not the coolant temperature, it should be code 49. Code 51 is the engine temperature so it is not surprising it stayed around 90C. The coolant on the other hand was rechecked and hit 116C which is on the high side. It looks like the coolant pump is the fault here.

 

You've got the green top temperature sensor, right? Original 2001 models (like mine) had the black one that liked to read flaky and hot.
Other than that, a flush and thermostat never hurt anyone (as lone as you get the bubbles out afterwards).
If you're replacing the pump, might as well replace the timing belt too.