A few late-model pickups and SUVs, such as Ford diesels and the Chevy TrailBlazer and others with the 4.2-liter inline Six, have an electronically controlled valve for the fan clutch. But even if it rotates three or fewer times the clutch could still be bad. You should feel some resistance and the fan may spin up to three times, depending on the ambient temperature. If the fan rotates more than five times, you can bet the clutch is bad. To confirm the diagnosis, start with this simple test: Spin the fan as hard as you can on an engine that has not been started that day. The first signs that a clutch fan is failing are obvious: The engine starts running hotter and a/c performance drops. Silicone fluid oozing past the bearing seal means the clutch must be replaced. 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). The hotter air causes the thermostatic spring to unwind and open the valve. As the engine warms up, the air flowing to the fan assembly becomes hotter. 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. The valve controls the flow of a viscous silicone fluid between chambers in the clutch assembly. The fan clutch operation is regulated by a valve that is opened and closed by a thermostatic spring. When the engine is cold, the fan runs much more slowly. When the engine is hot, the clutch fan runs nearly as fast as the engine. Clutch fans operate at different speeds under different conditions to help reduce drain on the engine and to save fuel. If your truck is like most, the cooling fan is mounted to its drive pulley via a clutch. When you move the throttle linkage to rev the engine to about three grand, fan speed picks up visibly, but it's still slow. There's no sign of belt slippage, but the radiator cooling fan barely seems to be spinning.
You start the engine, let it idle and make a visual inspection. The coolant level is right on, no hoses are leaking and the accessory belt is intact. Stretching your luck, you try the a/c again-and it works fine.Īt home, you lift the hood, puzzled.
#Clutch fan for cummins big cam 350 windows
You turn off the a/c and open the windows just as the traffic breaks and you speed up.
Then you realize that the air conditioner is blowing warm. You're crawling along in traffic and, despite the fact that your pickup bed is empty, the coolant temp is uncomfortably high.
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