I just finished putting everything back together in my 2002 R53 after changing the clutch and have an odd problem. When I turn the car on, the engine temperature gauge spikes to maximum. The cooling fans kick on and don't turn off even after the car is turned off (I have to disconnect the battery.) Is there a connector I missed or did I short out a wire somewhere?

 

Sounds like you have a short somewhere. Find the coolant temp sensor, and trace the wiring from it. Something is definitely not right.

 

Definitely sounds like a sensor short. Another possibility, but less likely, a stuck thermostat.

Drive Hard. Drive Safe. Keep Grinning.

 

Ended up being the connector getting pulled off the sensor. Hurray for previous owners breaking connector latches!

Though a new and fun problem has arisen where the outside temp sensor will drop to -40, then climb back up. Makes for amusing drives when when climate control switches to heat on a 90° day. (This seems like a loose wire/periodic short.)

 

Probably damaged the ambient temp sensor that is on long harness and snaps into back of lower grille on driver side.

FYI the one on ebay I purchased by year/make/model even though snapped into connector was not correct part....read wrong. I ended up needing one from dealer. ( not cheap either )

 

Probably. It did get swung around a bit during the process.