Hi all , my temp gauge gets to 90 deg as normal , however , when coasting , going down hill or accelerating hard it dips to about 85 on the dial then slowly rises and dips sporadically for the rest of the journey . The car drives fine and mpg is averaging 32.6 which I think is ok for an S3 . Audi have quoted £270 to change the thermostat but cannot guarantee this will sort the problem . What do you think , should I wait for it to get worse and the cause be more obvious or will the fault be harming the car due to possible overfuelling etc ? I want to be sure before spending 270 !