Auxillary fan always on

[bmwpower]

Ok...Just when I thought I had everything figured out and put back together, it looks like a I have another gremlin in this car.

History: new heater core due to previous coolant temp problems/fluctuations. Battery died in the several week long process from messing with the stepper motors and turning the car on/off/on/etc. So I get the jumper box out and give it a quick jump, starts right up. I had to do this a couple times since the car was out of commision for several weeks.

Now: It's all back together. I notice the OBC lights are off....hmmm...I notice the OBC cluster readout is dark....hmmmm. I still see the characters, but the bulbs must be blown out. Bulbs on order.

I drive the car to work this morning and I notice it's not running a smooth as it normally does. So I stop and checking things out. Everything looks kosher. Maybe I need new plugs? I dunno. Then I notice the aux fan is running. Turn the car off. Turn the car on again and it's running again. Cycle all the defrost swithc, cycle the A/C switch - nothing - still on.

The coolant temp gauge is fine, too, right in the middle. I'll have to check the car again once the coolant is cold to see if the fan comes on right away at startup.

Any idea what the hell this could be?

My only guess would be the thermo switch in the radiator or the coolant temp sensor and sender are fubar'd, giving me false readings.

[5kcstq]

One of the failure modes of the Aux. fan resistor is constant running of the fan. You might want to check yours. I had this happen on my M50tu. Wasn't expensive to replace, but was kinda a pita to do.

[bmwpower]

One of the failure modes of the Aux. fan resistor is constant running of the fan. You might want to check yours. I had this happen on my M50tu. Wasn't expensive to replace, but was kinda a pita to do.

It better not be the friggin resistor...

Forgot to mention: the fan is a BRAND NEW unit with new resistor. Installed several months ago, no problems until now.

I thought that when they fail, the fan does NOT work. At least that's what I've heard/seen first hand.

[moroza]

When resistors blow, they usually open the circuit, not reduce its load. Besides, that resistor is only for the low-speed fan circuit. I'd replace the radiator-mounted switch. It's easy to get to, and they're known to fail after the better part of 2 decades.

[bmwpower]

When resistors blow, they usually open the circuit, not reduce its load. Besides, that resistor is only for the low-speed fan circuit. I'd replace the radiator-mounted switch. It's easy to get to, and they're known to fail after the better part of 2 decades.

What?!? I was hoping it would it least make it 30 years....lol.

I was going to go out and play with the thing now at lunch to see what I could get it to do/not do.

[bmwpower]

Ok....

Pull the connector ----> fan goes off
Pull the high speed wire ----> wire breaks off...great ----> fan runs on low speed
Pull the connector ----> turn on A/C ---> low speed kicks on

It would appear the thermo switch is bad and my wire connections need attention.

Thermo switch on order, in addition to:
#3 (Quantity 3) of http://www.realoem.com/bmw/showparts.do?model=HD23&mospid=47408&btnr=61_1296&hg=61&fg=15&hl=6
#7 (Quantity 1) of http://www.realoem.com/bmw/showparts.do?model=HD23&mospid=47408&btnr=61_0543&hg=61&fg=15&hl=8

I hope these are the right parts, hard to tell, but they look right....

[robmpulse]

hummmmmmmmmmmm.................................... .................................................. ............................................

[eightynine535]

is the a/c system recirculate button on? I found when mine is on the AUX fan runs. weird.

[bmwpower]

is the a/c system recirculate button on? I found when mine is on the AUX fan runs. weird.

Yea, been there, done that. Button is not on in my case.

[moroza]

Just watch out for the small gush of coolant when you replace that switch. It sounds like the resistor, motor, and all other bits of the system are fine.