Question about 2002 Pontiac Aztek
Sounds like Clutch in your fan
The coolant level is right on, no hoses are leaking and the accessory belt is intact. You start the engine, let it idle and make a visual inspection. There's no sign of belt slippage.
If your car is like most, the cooling fan is mounted to its drive pulley via a clutch. Clutch fans operate at different speeds under different conditions to help reduce drain on the engine and to save fuel. When the engine is hot, the clutch fan runs nearly as fast as the engine. When the engine is cold, the fan runs much more slowly.
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.
Hope this helps!
Posted on Dec 14, 2008
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