I have an Audi A3 2001 1.9TDI engine code ASV and my temperature gauge has always been acting weird - goes to 100°C or higher and then drops back to 90°C.
I took my car to a local certified Audi mechanic and they told me that there is nothing wrong the cooling system itself. They said the problem lies with the temperature gauge which they also said it is a known problem on this models. They said that they can only replace the entire instrument cluster which would cost me about 800,00 € (almost half the value of my car ^_^), I of course declined. :)
Can I fix the temperature gauge by myself? What could be wrong with it? Is it the stepper motor? How can I diagnose this?
EDIT: I FORGOT TO MENTION that whenever the temperature goes above 90°C I gently hit above the instrument cluster and temperature immediately falls back down to 90°C, however I'm getting tired of hitting my car like this. Also it looks stupid when people pass me by and see me banging on the instrument cluster. ^_^