I have a 2000 PD115 A4, and recently my water temp gauge has decided not to move. However, my thermostat is only about 3 months old, and has been fine. I changed it when I first got the car and never had an issue since. My heater also works perfectly fine, and produces very warm air. Oil temp seems to be normal, but water now does not move at all, even after an hours drive. Using the climate control hidden menu, I can see that the value on 49 is 30c, and doesn't seem to move. The value on 51 appears to steadily climb to 90 and stay there. What do we think, coolant temp sensor? Stat faulty again? Agh!