auxiliary fan running only high speed and does not turn on

[boogie woogie]

Hi, im new hear and looking for some advice, hopefully i'll get some help.

I have a 96 318is and recently replaced my radiator. since that the auxiliary fan hasnt been running when the car heats up, and it starts to overheat. it seems the fan only runs on high speed. Ive check it on a 12v and it works. checked the relay and the fuse both are good. and ive even checked the sensor on the Rad, everything seems to be working except the fan wont turn on by itself. now ive done a temporary bypass and got it to to run at high speed all the time but I was wondering if anyone can help me figure out this problem? Im hoping its nothing too serious?!!?

[thejlevie]

Since the fan will run and the thermoswitch is good, the probable candidate is the fan speed resistor.

[boogie woogie]

is there anyway of fixing the fan speed resistor? the thermoswitch wont kick the fan in at all tho even tho its good?!?! just lets the car overheat!

[thejlevie]

is there anyway of fixing the fan speed resistor?

Yes, replace it.

The aux fan should only come into the picture when the A/C is on and the car is stopped or moving at low speed. If the engine wants to overheat with the A/C off you've got other problems (bad thermostat or waterpump, clogged radiator, head gasket leak, etc).