Hi, I had a similar problem. My gauge didnt register any temp change (from 60) intermitently - I presumed this wasnt the water pump as it wasnt registering high! So last night I changed the Coolant Temp Sensor which was easy.
However now it does register a temp but seems very reluctant to go abouve 70, it occasionally pushes round to 80 but then back down to 70! Is this standard on the A3 or should it just quickly warm upto 90 and stay there?
Im a bit stuck, and really [censored] as I was hoping to avoid these annoying niggles with my new car. I will work on it and if i get a fix I'll let you know, if you fix yours please update here !!!
A possible idea I had was a air in the rad (after changing sensor) giving changing results, or possibly the temp sensor sent was faulty (doubtful). If anyone can tell me where the bleed valves are and if i need an expansion tank to bleed the rad.
Regards.
A3 T, 1997 67k