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  • Aux Fan not turning on

    Hello, I just noticed that my aux fan never turns on to cool the engine. I thought the only fan that cooled the engine was the one thats turned by the engine. Never owned a car with a fan thats turned by the engine. When I leave the car at idle the water temp goes to over heat. I have No problems driveing around and the car stays cool. When I turn on the a/c the aux fan does turn on. I checked the fuses and they look good. I did a search but there are no pics on what to look for. What should I do next to solve this problem? thanks

  • #2
    You probably toasted the fan resistor, which is located right by the fan. Remove the front bumper cover (two bolts), and you can see it.

    BMW makes a resistor repair kit that you will find in the parts diagrams. Or, if your fan is toast (like mine was), just replace the clunky, heavy dead fan with a lightweight, high-efficiency SPAL unit.
    2003 Mitsu EVO VIII - 2.0L / 600+whp
    1988 BMW M3 turbo - Work in progress. . .
    1986 SVO Mustang - Work in progress. . .

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    • #3
      I'd do a few tests before swapping parts.

      Feed 12v directly to the fan. If it works then the problem is upstream. Unplug the thermoswitch connector on the thermostat, and bridge two of the contacts for low speed, and the other two for high speed. That should trigger the relays. If the fan doesn't work, then your problem lies in the relays. If the fan works, then the problem is the thermoswitch.

      The above tests take about 15 minutes. BTW Does the electric fan still turn, or is it frozen???


      [email protected]

      1969 2002 racecar
      1989 M3 racecar
      e39 Touring

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      • #4
        I'm interested in this as I have a similar problem. in case you need to remove the front bumper, is it really just the two 19mm nuts and that's it? Nothing on the bottom or along the back to remove?

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        • #5
          As per my recollection, that was it. Of course, you need to be mindful of the foglight wiring and such.

          When I went to turn my fan by hand, there was a lot of resistance. Apparently, it toasted a bearing, and that was that. I replaced it with a SPAL - costs less, better design.
          2003 Mitsu EVO VIII - 2.0L / 600+whp
          1988 BMW M3 turbo - Work in progress. . .
          1986 SVO Mustang - Work in progress. . .

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          • #6
            Originally posted by Ted B View Post
            You probably toasted the fan resistor, which is located right by the fan. Remove the front bumper cover (two bolts), and you can see it.

            BMW makes a resistor repair kit that you will find in the parts diagrams. Or, if your fan is toast (like mine was), just replace the clunky, heavy dead fan with a lightweight, high-efficiency SPAL unit.
            I dont think the fan resistor has worked since i bought the car. The aux fan does work when I turn on the a/c


            - - - - - - - - - - - - - - - - - - - - - - - - - AUTOMERGED! There's no thread "bumping" or "double posting" within a 24hr period. - - - - - - - - - - - - - - - - - - - - - - -


            Originally posted by LeeVuong View Post
            I'd do a few tests before swapping parts.

            Feed 12v directly to the fan. If it works then the problem is upstream. Unplug the thermoswitch connector on the thermostat, and bridge two of the contacts for low speed, and the other two for high speed. That should trigger the relays. If the fan doesn't work, then your problem lies in the relays. If the fan works, then the problem is the thermoswitch.

            The above tests take about 15 minutes. BTW Does the electric fan still turn, or is it frozen???
            This sounds great but I do not know how to feed 12v directly to the fan, I do not know where the thermoswitch.
            Last edited by feakara1; 10-14-2008, 12:06 PM. Reason: Automerged Doublepost

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            • #7
              I had a similar problem a few months ago. I replaced the resistor and got a new low temp 81/88 degree switch and problem was fixed. The low speed is supposed to turn on without AC at around half mark.

              Don't drive your car if it goes to the redline when on stop. But if you have no choice just keep on revving the motor even when on stop to get that engine fan to cool the motor. Try checking your fan clutch also if it is working fine.

              I have a new problem now that the auxiliary fan is always on even when the engine has not started yet. I still have to diagnose that problem.

              HTH

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              • #8
                Originally posted by jpchan View Post
                I had a similar problem a few months ago. I replaced the resistor and got a new low temp 81/88 degree switch and problem was fixed. The low speed is supposed to turn on without AC at around half mark.

                Don't drive your car if it goes to the redline when on stop. But if you have no choice just keep on revving the motor even when on stop to get that engine fan to cool the motor. Try checking your fan clutch also if it is working fine.

                I have a new problem now that the auxiliary fan is always on even when the engine has not started yet. I still have to diagnose that problem.

                HTH
                thanks for the advice. the aux fan only works when the a/c is turned on. IT does not turn on when the water temp reaches half way or 3/4. I think it may be the dual temperature switch.

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                • #9
                  At the front right side of your motor in line with the radiator hoses is the "grenade" it's the metal housing for the thermostat. There should be 2 (I believe) sets of wires going to 2 sensors one set has 3 wires. Those are the low and high speed circuits for your electric fan. Those wires broke on my car and the PO put in a $.49 plug in instead of the replacement sensor/switch. After I figured out what had been done, I replaced the sensor and added pigtails to the toasted and broken wires. I also found that a cap end of the spark plug wire works to cover the 3-wire-Home-Depot-black-jacket-same-diameter-as-the-original wire I used for the pig tail. I separated the female spade connectors with heat shrink tubing. I fired up the car when it was cold and checked the sensor/switch to see which circuit closed first for the low temp fan seed with a multimeter. The other sensor terminal proved correct for the high speed. Check to see if the wires have frayed insulation at that grenade. Good luck.

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                  • #10
                    Originally posted by ahlem View Post
                    At the front right side of your motor in line with the radiator hoses is the "grenade" it's the metal housing for the thermostat. There should be 2 (I believe) sets of wires going to 2 sensors one set has 3 wires. Those are the low and high speed circuits for your electric fan. Those wires broke on my car and the PO put in a $.49 plug in instead of the replacement sensor/switch. After I figured out what had been done, I replaced the sensor and added pigtails to the toasted and broken wires. I also found that a cap end of the spark plug wire works to cover the 3-wire-Home-Depot-black-jacket-same-diameter-as-the-original wire I used for the pig tail. I separated the female spade connectors with heat shrink tubing. I fired up the car when it was cold and checked the sensor/switch to see which circuit closed first for the low temp fan seed with a multimeter. The other sensor terminal proved correct for the high speed. Check to see if the wires have frayed insulation at that grenade. Good luck.
                    Im going to check those wires tomorow. I have a question with the fan clutch. When you first turn on the car and it is cold, should the belt driven fan turn? Am I correct in saying that when the engine is cold the belt driven fan should not turn until the engine heats up.

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                    • #11
                      Originally posted by feakara1 View Post
                      Im going to check those wires tomorow. I have a question with the fan clutch. When you first turn on the car and it is cold, should the belt driven fan turn? Am I correct in saying that when the engine is cold the belt driven fan should not turn until the engine heats up.
                      The clutch driven fan in my car is always on. I would check your clutch ot make sure it is functioning

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                      • #12
                        Originally posted by R6Elmo View Post
                        The clutch driven fan in my car is always on. I would check your clutch ot make sure it is functioning
                        what is the best way to check it? I have heard about the newspaper test, not sure how to do it

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                        • #13
                          Originally posted by feakara1 View Post
                          what is the best way to check it? I have heard about the newspaper test, not sure how to do it
                          The engine fan should be turning even at idle and still strong enough to shred a newspaper (not sure what thickness though) I used one whole section and it was shredded up with my new fan clutch installed.

                          Well, if the engine fan is not turning when the engine is running then there is no need to do that test. If both your fans are not turning do not drive the car! I would get somebody to look at it at home or have it towed to your shop of choice.

                          HTH

                          Patrick

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                          • #14
                            When the fan clutch gets defective, usually it stats ON all the time. Making that whirling noise under acceleration. But as was said, when in doubt, don't drive the car with two bad fans. Not worth an engine rebuild due to overheated motor.


                            [email protected]

                            1969 2002 racecar
                            1989 M3 racecar
                            e39 Touring

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                            • #15
                              Originally posted by LeeVuong View Post
                              When the fan clutch gets defective, usually it stats ON all the time. Making that whirling noise under acceleration. But as was said, when in doubt, don't drive the car with two bad fans. Not worth an engine rebuild due to overheated motor.
                              THe fan is always turning. IT does not make noises etc. I did the newspaper test with a whole newspaper. I have read now that you use only one newspaper sheet rolled up. I think I will just replace the fan clutch, the dual temp switch and flush the coolant with new fluid.

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