Quote:
Originally Posted by ryguy
The fan clutch is more loose when it's cold, and gets tighter as the vehicle heats up. The inside is filled with hydraulic oil that expands when it heats, pushing the clutch together. It should still have good resistance when it's cold, if not there's likely no hydraulic oil in the clutch anymore. That's wierd that changing the fan clutch made the noise go away.
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there is a thermostatic spring on the stock clutches:
The fan clutch operation is regulated by a valve that is opened and closed by a thermostatic spring. The valve controls the flow of a viscous silicone fluid between chambers in the clutch assembly. When the engine is cold, the clutch is essentially disengaged, which is why the fan runs at its slowest compared to the engine's speed. As the engine warms up, the air flowing to the fan assembly becomes hotter. The hotter air causes the thermostatic spring to unwind and open the valve. Silicone fluid from the reservoir chamber flows into the main chamber, engaging the clutch, and the fan spins faster (though it's still slightly slower than the engine).