I've read all the posts on the auxiliary fan next to the radiator. I know that the bearings are loose. I am getting ready to have a local audi specialist install a new one (found online sites selling for $133).
The only thing I question is that my temp guage recently stopped working and I don't know if this will have any repurcussions. Also, the loud fan goes into F22 fighter mode even now in the dead of winter when the heater is on (even right when i start the car). As soon as I turn the heat off, it turns off as well. It will turn off after driving for awhile too. Does this make any sense? I'm really confused by this. Any thoughts???

199 Audi A6 2.8 Quattro

 

fan install is pretty easy. remove two holding screws then twist and fan is in hand. Of course the wiring clips are a major pita.

the fan always runs when the a/c is on. Your gauge problem is unrelated. You just need to replace the temp sensor, cheap part.

I have still not figured out why the fan goes into turbo mode at times. Mine started doing it more as the fan control unit failed.