Saturday Mechanic - Fan Clutch Replacement

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KEYWORDS

• maintenance
• Saturday Mechanic
• transmission

You're crawling along in traffic and, despite the fact that your pickup bed is empty, the coolant temp is uncomfortably high. Then you realize that the air conditioner is blowing warm. You turn off the a/c and open the windows just as the traffic breaks and you speed up. The coolant temp drops. Stretching your luck, you try the a/c again--and it works fine.

LISTLESS AND LAZY
At home, you lift the hood, puzzled. 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, but the radiator cooling fan barely seems to be spinning. When you move the throttle linkage to rev the engine to about three grand, fan speed picks up visibly, but it's still slow.

If your truck 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).

NULL.

Click to enlarge
A broken or weakened thermostatic spring in the clutch hub cannot be replaced or repaired.

Click to enlarge
Silicone fluid oozing past the bearing seal means the clutch must be replaced.

Reader Comments

5. RE: Saturday Mechanic - Fan Clutch Replacement
Testing a clutch hub

4. RE: Saturday Mechanic - Fan Clutch Replacement
Wow. That was a fabulous explanation. Is a fan clutch supposed to last more than 50,000 miles? I had one replaced two years ago, and had to just do it again.

3. RE: Saturday Mechanic - Fan Clutch Replacement
i want to get n information that what is clutch resently indian vehicals has started to use clutch fans how can i make this clutch? Is it possible

2. RE: Saturday Mechanic - Fan Clutch Replacement
Does a fan clutch make a noise when is goes bad?

1. RE: Saturday Mechanic - Fan Clutch Replacement
Thank You, Thank You very helpful.

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