my 2006 Audi A4 3.0 conv. temp seems to be running normal but after I shut off the car the fan will come on (maybe 10 minutes later) and not shut off until the battery is drained.

 

Sounds like the classic fan temp sensor problem. There is a $30 sensor in the radiator that controls the fans. Sometimes when this sensor goes bad, it will turn the fans on even if the car is not hot. The circuit is live all the time so.. Look for an electrical connection on either side of the radiator reservoirs. That should be it. You can get the sensor at any automotive parts store. You will have to drain the coolant to replace it.