I was washing the engine compartment tonight.
After I washed the engine I always start it to burn off any
water. I was standing there watching the marvel of the N62 run.
As the engine warmed to operating temperature, I noticed the Aux Fan was
really spinning. It is warm here but not Texas warm (yet).

My sold wagon E39 528it just yesterday had the same screaming Aux Fan.
I swapped out the coolant outlet temperature sensor to a new unit.
It was from the factory dated early 2000!
New sensor calmed the Aux Fan to a normal RPM.

Tonight, I had to do the same for my E53 X5. Replaced the outlet temperature
sender (lower radiator hose) and fixed my screaming Aux Fan.
It was dated November of 2003. I think I got my money's worth.

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2003 4.6is X5
2003 525it
2003 E53 X5 Standard shift