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Electric fan coming on at start-up? 700

posted by  pbrown on  Fri Apr 11 05:17 CST 2003
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Is the electric fan supposed to come on at start-up? I have noticed a rushing humming noise when the idle is high at the initial cold start but had no idea what it was until I happened to look through the grill and saw the fan spinning. Is my fan running or is it windmilling with the engine fan?

If it is powered up, why is this necessary. The noise only happens for about 10-15 seconds.








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    Electric fan coming on at start-up? 700

    posted by  someone claiming to be bob on  Fri Apr 11 20:49 CST 2003 [RELATED]

    The noise you hear is the belt driven fan pulling air across the radiator. It will do this for a few seconds till the fluid in the viscous clutch allows it to freewheel. The electric fan is windmilling.








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    Electric fan coming on at start-up? 700

    posted by  spasske on  Fri Apr 11 07:53 CST 2003
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    last visit: Thu Oct 23 10:11 CST 2014
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    The fan turns on when the thermal switch near the top right of the radiator closes. The fan starting is based soley on the temperature of the radiator (with key on) . You can easily jumper the switch to show you what it looks like when the fan is powered on. It goes at a pretty good rpm so I don't think your windmilling fan is on.

    Does your temperature gauge point straight up when the engine is warmed up?

    --
    Paul NW Indiana '89 740 Turbo 103,000








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      Electric fan coming on at start-up? 700

      posted by  pbrown on  Fri Apr 11 09:51 CST 2003
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      This happens with a cold engine. So I don't know why the thermal switch would be closing with a cold engine. Maybe the relay is closing for some unknown reason.








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        Electric fan coming on at start-up? 700

        posted by  spasske on  Sat Apr 12 05:08 CST 2003
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        last visit: Thu Oct 23 10:11 CST 2014
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        The relay always picks up with the key on. The switch then completes the circuit. Just pull the two connectors off the switch and measure the resistence of the switch. Low resistence (with cold engine) means you have a bad switch.

        --
        Paul '89 740 Turbo 102,000







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