Thread: Fan clutch.
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Old 10-06-2012, 03:14 PM   #15
jdstrickland
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Join Date: Apr 2010
Location: Murrieta, CA
Posts: 7,442
My Ride: '94 325iC & '00 323i
Take the belt off and run the car for a couple of minutes. Do not allow it to overheat, but without the belt you will know if the noise comes from the belt/pulley system, or something else.

The fan clutch is almost never the source of noise of any kind. Noises from the area will come from the waterpump, the idler and tensioner pulleys, and the power steering pump and alternator.

When you start the car on a cold engine, there is a very loud fan that pushes fresh air into the exhaust stream to help the CATs do what CATs do but don't do very well while cold. After the CATs heat up, the fan turns off and stays off until the next Cold Engine Start. If you hear a loud fan on the first start of the day, or the first start after a long period of being parked, then the noise is 1.) normal, and 2.) costly to fix, and 3.) completely unimportant to the car so you can wait for failure of the fan -- which will be noted by the Check Engine light and a code (P1423, or something like that). You can wait for the Secondary Air Pump to completely fail and the car won't care one bit. The Smog Shop guy will care, but the car won't.

Last edited by jdstrickland; 10-06-2012 at 03:14 PM.
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