Home » GM 6.5 » GM/Detroit 6.5L – FAN CLUTCH DIAGNOSlS


Fan noise is sometimes evident under the following normal conditions.
• When the clutch is engaged for maximum cooling.
• During the first 15 seconds to one minute after start-up until the clutch can re-distribute the sili­cone fluid back to its normal disengaged operating condition (after overnight settling).
Fan noise or an excessive roar will generally occurcontinuously under all high engine speed conditions (2500 rpm and up) if the clutch assembly is locked up due to an internal failure. If the fan cannot be rotated by hand or there is a rough grating feel as the fan is turned, replace the clutch. Refer to “ Fan and Fan Clutch Replacement.”

Check a loose fan assembly for wear and replace as necessary. Under various temperature conditions, there is a visible lateral movement at the tip of the fan blade.
Approximately 6.5 mm (1/4 inch) maximum lateral movement measured at the fan tip is allowable. This is not cause for replacement.

The fan clutch operation is affected by fluid leaks which may occur in the area around the bearing assem­bly. If leakage appears, replace the fan clutch. Refer to “Fan and Fan Clutch Replacement.”

1. Start with a cool engine to ensure complete fan clutch disengagement.
2. If the fan and clutch assembly free-wheels with no drag (revolves more than five times when spun by hand), replace the clutch. Refer to “Fan and Fan Clutch Replacement.” If the clutch performs proper­ly with a slight drag, go to step C.
• Testing a fan clutch by holding the small hub with one hand and rotating the aluminum hous­ing in a clockwise/counterclockwise motion will cause the clutch to free-wheel, which is a nor­mal condition when operated in this manner.
This should not be considered a test by which replacement is determined.
3. Position a thermometer so it is located between the fan blades and the radiator. This can be achieved by inserting the thermometer sensor through one of the existing holes in the fan shroud or by placing it between the radiator and the shroud. On some models, it may be necessary to drill a 5-mm (3/16-inch) hole in the fan shroud to insert the ther­mometer.

NOTICE: Check for adequate clearance between fan blades and the thermometer sensor before starting engine, as damage could occur.
4. With the thermometer in position, cover the radiator grille sufficiently to induce a high engine tempera­ture, start the engine, turn air conditioning on, and operate at 2000 rpm.
5. Observe thermometer reading when the clutch engages. It will take approximately 5 to 10 minutes for the temperature to become high enough to allow engagement of the fan clutch on gasoline engines and 15 to 20 minutes on diesel engines.

This will be indicated by an increase or roar in fan air noise and by a drop in the thermometer reading of approximately 3°C to 10°C (5°F to 15T).
• If the clutch did not engage between 65°C to 96°C (150°F to 205T) the unit should be replaced. Be sure the fan clutch was disen­gaged at the beginning of the test.
• If no sharp increase in fan noise or temperature drop was observed and the fan noise level was constantly high from start of test to 88‘C (190T), the unit should be replaced. Do not continue the test past a thermometer reading of 96°C (205°F) to prevent engine overheating.

6. As soon as the clutch engages, remove the radia­ tor grille cover and turn the air conditioning off to assist in engine cooling. Run the engine at approxi­mately 1500 rpm.
7. After several minutes, the fan clutch should disen­gage as indicated by a reduction in fan speed and
roar. If the fan clutch fails to function as described, it should be replaced.


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