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fan clutch always engaged

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basic question, kinda new to the engine layout of my silverado, so apologies in advance if the ? sounds redundant.


2001 silverado extended cab, 4.8 motor, 70k miles


it seems to me as if the fan clutch always seems engaged, even at cold startup, under even part throttle, I can hear the fan roar as if it's engaged right from strtup. My only comparrison to RWD layouts with attached fans (non electric) was my buddies mopar, and you really never heard the fan run unless the thing was hot. You could visually see that the fan was rotating slower than the engine RPM and could see it accelerate as the clutch engaged.


On the silverado the fan seems to be at normal engine RPM all the time.


is this normal behavior for these units? or should I be investigaiting a possible clutch failure. is there a thermistor or circuit that I can check for voltage or resistance to see if the clutch is engagning/disengaging?

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Fan Clutch Diagnosis

Fan Noise

Fan noise is sometimes evident under the following conditions:


• When the clutch is engaged for maximum cooling.


• During the first 15 seconds to 1 minute after start-up until the clutch can redistribute the silicone fluid back to the fluid's normal disengaged operating condition (after overnight settling).


Fan noise, or an excessive roar, generally occurs continuously under all high engine speed conditions (2500 RPM and up) if the clutch assembly locks up because of an internal failure. If you cannot rotate the fan by hand, or if there is a rough grating feel as the fan is turned, replace the clutch. Refer to Fan Clutch Replacement .



Under various temperature conditions, a lateral movement is visible at the tip of the fan blade. About 6.5 mm (1/4 in) maximum lateral movement, measured at the fan tip, is allowable. Replacement of the fan clutch is not necessary.


Ensure that the fan blade is installed properly. If the fan is installed incorrectly, the fan will cause an overheating problem.


Silicone Fluid Leaks

Small fluid leaks, occurring in the area around the bearing assembly, do not affect the operation of the fan blade clutch.


If leakage appears replace the fan clutch. Refer to Fan Clutch Replacement .


Engine Overheating

In order to ensure complete fan blade clutch disengagement, begin testing with a cool engine.

If the fan blade clutch assembly free wheels with no drag, (revolves more than 5 times when spun by hand), replace the fan clutch. Refer to Fan Clutch Replacement . If the clutch performs properly with a slight drag, refer to step 3. Testing a fan blade clutch by holding the small hub with 1 hand, and rotating the aluminum housing in a clockwise/counterclockwise motion, causes the clutch to free wheel. Consider this operation normal and this test should not determine replacement.

Perform the following steps:

Sufficiently cover the radiator grille in order to induce a high engine temperature.

Start the engine.

Turn on the air conditioning (A/C) if equipped.

Operate the engine at 2000 RPM.

Inspect the coolant temperature when the clutch engages. Allow about 5 to 10 minutes for the temperature to become high enough in order to engage the fan blade clutch. This will be indicated by an increase, or roar, in fan air noise and by a drop in the coolant temperature reading of about 3-10°C (5-15°F).

- If the clutch did not engage between 110-121°C (230-250°F), replace the assembly. Ensure that the fan blade clutch was disengaged at the beginning of the test.


- If you did not observe a sharp increase in the fan noise or a temperature drop, and the fan noise level was constantly high from the start of the test, replace the assembly. Do not continue this test past a thermometer reading of 121°C (250°F) in order to prevent engine overheating.


When the clutch engages, do the following steps:

Remove the radiator grille cover.

Turn off the A/C in order to assist in engine cooling.

Operate the engine at about 2500 RPM.

After several minutes, the fan blade clutch should disengage as indicated by a reduction in fan speed and roar. If the fan blade clutch fails to function as described, replace the fan blade clutch. Refer to Fan Clutch Replacement .

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