Bad Fan Clutch Troubleshooting Case Study (GM 4.8L, 5.3L, 6.0L)

Fan Clutch Troubleshooting Summary

It used to be that checking a thermal fan clutch was an easy matter since they all could be very easily locked into their Engaged Mode by simply moving the end of the bimetallic coil to another spot on the fan clutch assembly.

Nowadays, most modern thermal fan clutches don't have that feature anymore but it doesn't mean that they can't be tested.

If you're able to think outside the box and get a little creative, you can still manually lock up the fan clutch to test it. Here are three other very important things you should also check on the fan clutch assembly:

  1. FAN NOISE at all times, whether the engine is at normal operating temperature or not:
    • It's normal to hear a roaring sound (as the air gets pulled across the radiator) when you first start up a cold engine.
    • This roaring sound, with a correctly functioning fan clutch, dissipates after a few minutes (as the clutch re-distributes the silicone fluid back to its normal disengaged mode).
    • It's when the roaring sound continues under all high engine speed conditions ( 2500 rpm and up ) that IS NOT normal and indicates that the fan clutch assembly is locked up due to an internal failure.
    • This condition can be further tested with the engine off and as you turn the fan blades by hand, you'll notice that the fan cannot be rotated and/or you'll feel a rough grating as you turn the fan by hand.
  2. LOOSENESS (excessive lateral play):
    1. With the engine running and under various temperature conditions, there's a visible lateral movement that can be observed at the tip of the fan blade.
    2. With the engine off, you can grab the tip of the fan blade and physically check this movement.
    3. The amount of play (movement) is normal up to a certain point (since this play is due to the type of bearing used). Approximately 1/4" maximum lateral movement measured at the fan tip is allowable depending on make and model (you'll need to check the manufacturer's specifications to see if the lateral movement of the fan clutch on your vehicle is normal).
  3. SILICONE FLUID LEAK from the bearing area:
    • Silicone fluid leaking is a sign that the fan clutch needs to be replaced.

Remember, check these things also:

  1. Water pump for coolant leaks.
  2. Radiator for coolant leaks.
  3. Operation of thermostat.
  4. Indications that the head gasket has blown.

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Related Test Articles

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