Diagnosing fan clutch

Discussion in 'General Motoring' started by Duong Nguyen, Nov 20, 2003.

  1. Duong Nguyen

    Duong Nguyen Guest

    My 740GLE overheats badly when idling in hot weather but OK when
    moving moderately fast. Except for the idle speed that is rather
    erratic (some day exactly where it should be around 750 rmp, other
    days at 500 or 900 or switching to different speeds in between) there
    is no other problem. Of the few items I have to check to fix this
    overheating the thermal fan clutch seems to be the hardest. When the
    car is cold there is a resistance when I try to turn it by hand (it
    won't spin.) This morning when I got to work (after some 30 km drive)
    it seems to offer the same resistance when I tried to spin it. Is this
    indicative of a faulty fan clutch? Not knowing how stiff a hot fan
    should be I have no clue as to whether the fan clutch is good or bad.
    Can somebody tell me if it should offer subtantially more resistance
    once the car has reached normal temperature or does this "more
    resistance" only occurs when the car is over the normal temperature
    range and only when hot air is blowing past it. I will do this "cover
    it with a blanket test" later if this is considered inconclusive.
    Duong Nguyen, Nov 20, 2003
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  2. Duong Nguyen

    Duong Nguyen Guest

    Now that I have re-read the message is rather misleading. What I mean
    is "it won't spin freely." It does move with a slight resistance.
    Duong Nguyen, Nov 20, 2003
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  3. Duong Nguyen

    Mike F Guest

    What I do to test these is use a balled up rag to stop the fan with the
    engine at idle. When it's cold, the rag stops the fan quite easily, use
    this as a baseline. When it should be locked up (engine temp above
    normal) this method won't stop the fan, don't try too hard. Watch your
    Mike F, Nov 20, 2003
  4. Before investigating the fan, did you check the radiator?

    If the exterior of the radiator is full of insects, dust, leaves and
    whatever may get stuck in there, it tends to block the air flow,
    typically causing overheating when idling.

    If the radiator is old try cleaning it with a hose, spraying water from
    the engine compartment through the radiator towards the front of the
    car. Use a moderate pressure since the aluminum radiators are not too


    240 Turbo Wagon '84 200 K Miles
    940 Wagon '92 150 K Miles
    on Swedish roads
    Gunnar Eikman, Nov 20, 2003
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