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Topic Review (Newest First)

  • 12-31-2010, 01:34 AM
    Steve G

    Well, there is one cheap fix.

    Connect the low speed and high speed power circuits to the high speed wire at the fan.

    If you do this, the fan will run on high speed if either circuit (high or low) turns on.

    This is better for cooling the engine than having only the high speed circuit working. Also, the AC uses the low speed fan (mostly) but if it turns on the high speed fan the AC works better.

    I'm using an inexpensive aftermarket rad fan on my 325. It only has one speed. It's been working well for about 4 years. I also removed the clutch fan at the same time.

  • 12-30-2010, 12:31 PM
    wicked94pgt

    Re: Radiator auxiliary Fan is only switching on to one

    If you checked voltage at the fan connector that should be good enough. At that point I would have powered the fan directly as well just for good measure. The only other problem you could have now is the connector actually not making contact, which is unlikely.

    Much more likely that the fan is dead. It's probably that resistor as you've suggested, or maybe the wiring between the connector and the resistor, or between the resistor and the fan motor itself. I don't know if you can disassemble the fan to check any of that internal wiring, but it could be worth a try.

    The resistor is not "serviceable", as in there is no BMW part number for the resistor by itself. You might be able to find a manufacturer part number on the resistor and then track down a replacement on the open market, like some people have done to replace blower fan bearings. But I'm guessing it's a specialized resistor made specifically by or for the fan manufacturer, and there's a good chance you won't be able to find it for sale anywhere by itself.

    It might be possible to find an equivalent resistor that you can shoe-horn in place somehow. Short answer: I don't think there's any easy cheap fix for this.

    1996 BMW 328i
    2003 BMW F650CS - R.I.P. 8/25/2004
    2005 Suzuki SV650S - 3/26/2005
  • 12-25-2010, 02:43 PM
    jim318is

    Re: Radiator auxiliary Fan is only switching on to one

    With the ignition on I disconnected the terminal at the thermal switch and I shorted out the low temp/low speed wire. (simulating the low speed fan kicking on) then I disconnected the terminal at the fan and checked for voltage, and there was 12 volts. telling me that everything up to the fan is working.

    On the back of the fan there is a long tube thing, Im guessing that is a resistor...

    Can that go bad only on the low speed side of the circuit?

    Can I replace the resistor without replacing the entire fan?

  • 12-22-2010, 11:42 AM
    wicked94pgt

    Re: Radiator auxiliary Fan is only switching on to one


    I'm not familiar with the 318 but I think my 328 has different relays for low and high speed. I recall swapping some other relay in for the low speed relay.

    Anyway, when I say power the fan directly I mean directly - not through the relays. Apply power at the terminals on the fan chassis. It is kind of a PITA at least on a 328. I'm sure you can do it without removing the fan but it's really hard to tell which terminals you're clipping onto. It's much easier and more reliable testing it out of the car, but removing it is a bit of a process just for a quick check. Either way that's the only way to really know if the fan itself is working or you have some other problem.

    If the fan works check the wiring between the relay and the connector at the fan.

    1996 BMW 328i
    2003 BMW F650CS - R.I.P. 8/25/2004
    2005 Suzuki SV650S - 3/26/2005
  • 12-19-2010, 09:49 PM
    jim318is

    Re: Radiator auxiliary Fan is only switching on to one

    No, but i hear the relay clicking..
    And so i switched the high speed and low speed relays and the same thing happened. High speed works but low doesnt.
  • 12-16-2010, 06:06 PM
    wicked94pgt

    Re: Radiator auxiliary Fan is only switching on to one

    Does the fan work at low speed if you power it directly?1996 BMW 328i
    2003 BMW F650CS - R.I.P. 8/25/2004
    2005 Suzuki SV650S - 3/26/2005
  • 12-16-2010, 05:18 PM
    jim318is

    Radiator auxiliary Fan is only switching on to one

    My understanding of the auxiliary fan is it two speeds (high and low) and turns on at two different temps 90c for low and 99c for high (or something like that)Ö

    Now my problem is (if I understand the operation correctly) that the fan is only turning on at high speed when the coolant is running hot temp.

    Any ideas on why the low temp isnít kicking on the low speed would be great.

    Its not the fuse and its not the relays.

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