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Thread: '86 K75 How do I test fan?

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  1. #1
    On the Road
    Join Date
    Jul 2006
    Location
    Mckinleyville, CA
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    '86 K75 How do I test fan?

    New to me '86 K75. How do I test for the fans functioning? Does it come on at start-up, idling, or just when the bike is very hot? I live in a cool climate and it has not come on yet.
    Thanks much,

  2. #2
    3 Red Bricks
    Join Date
    Jan 2007
    Location
    Pleasanton, Ca.
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    3,383
    Stephen,

    Please read: http://www.bmwmoa.org/forum/showthre...r-thread-title!

    In the future, when you are starting a thread, please include that info IN THE TITLE. I have added that info to you title this time.


    As to your question:

    FIRST check that the fan blade spins FREELY. You can remove the air snorkle and reach in and spin the blade. It SHOULD have no resistance. If it does, it is probably bad.

    If your horn and turn indicators work, the fuse for the fan is still good.

    If the fan spins freely, you can test the operation by letting your bike idle for about 10 minutes. The fan should come on BEFORE the overtemp light comes on.

    K75 fans come on so infrequently, due to a cooling system basically designed to cool a K100, that crud gets into the bushing in the fan motor. Then 6 months later in the middle of a heat wave in July, while stopped at a long light, the temp sensor calls for the fan. The crud in the bushing causes enough drag that the fan motor gets hot, melting the PLASTIC brush holders and frying the fan motor! New motors can be purchased from Euromotoelectrics or Beemerboneyard for around $70.

    Every couple of months and BEFORE any long trips, check the fan blade for free spinning.



    Last edited by 98lee; 06-10-2013 at 06:35 PM.
    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  3. #3
    Benchwrenching PGlaves's Avatar
    Join Date
    Oct 2003
    Location
    "Big Bend" TX
    Posts
    8,659
    Remove the fuel tank. The connector for the fan motor is clearly visible. On most K75 bikes, so is the battery.

    Connect one jumper lead to the positive wire to the fan. Connect a second jumper to the ground lead from the fan.

    Connect the positive lead to the positive post of the battery.

    Connect the ground jumper to a good ground point on the frame. The capscrew with all the brown wires connected on the left side of the backbone would be a good choice.

    Observe whether the fan starts (fan good) or fails to start (fan bad).

    That tests the fan motor.

    Letting it idle until warm enough to turn on the fan tests the whole system: sensor, relay, wiring, motor, etc.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

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