I have an 05 Mini Cooper s and just had to replace Throwout bearing. Because of this I went ahead and replaced clutch while I had it apart. Once everything was back together I started the car and the temp gauge was maxed out with the light on. The fan turned on within seconds of starting. When I turned the car off the fan wouldn't stop, until I tirned key back to on position. Had to unplug the the power to the fan.. If anyone knows what would be causing this or how to fix it it would be greatly appreciated!

 

The temperature sensor for the temp gauge is on the cylinder head, just about the transmission housing. Did you check that you got the wire reattached correctly?