Fan Clutch: Testing and Inspection

Bi-Metallic Coiled Spring Removal:

FAN DRIVE CLUTCH TEST
Do not operate the engine until the fan has been first checked for possible cracks and separations.
Run the engine at a fast idle speed (1000 RPM) until normal operating temperature is reached. This process can be speeded up by blocking off the front of the radiator with cardboard. Regardless of temperatures, the unit must be operated for at least five minutes immediately before being tested.
Stop the engine and, using a glove or a cloth to protect the hand, immediately check the effort required to turn the fan. If considerable effort is required, it can be assumed that the coupling is operating satisfactorily. If very little effort is required to turn the fan, it is an indication that the coupling is not operating properly and should be replaced.
If the clutch fan is the coiled bimetallic spring type, it may be tested while the vehicle is being driven. To check, disconnect the bimetal spring, Fig. 4, and rotate 90° counterclockwise. This disables the temperature-controlled, free-wheeling feature and the clutch performs like a conventional fan. If this cures the overheating condition, replace the clutch fan.




FAN CLUTCH NOISE
Fan clutch noise can sometimes be noticed when clutch is engaged for maximum cooling. Clutch noise is also noticeable within the first few minutes after starting engine while clutch is redistributing the silicone fluid back to its normal, disengaged operating condition after settling for long periods of time (overnight). However, continuous fan noise or an excessive roar indicates the clutch assembly is locked-up due to internal failure. This condition can be checked by attempting to manually rotate fan. If fan cannot be rotated manually or there is a rough, abrasive feel as fan is rotated, the clutch should be replaced.

FAN LOOSENESS
Lateral movement can be observed at the fan blade tip under various temperature conditions because of the type bearing used. This movement should not exceed 1/4 inch (6.5 mm) as measured at the fan tip. If this lateral movement does not exceed specifications, there is no cause for replacement.

CLUTCH FLUID LEAK
Small fluid leaks do not generally affect the operation of the unit. These leaks generally occur around the area of the bearing assembly, but if the leaks appear to be excessive, engine overheating may occur. Check for clutch and fan free-wheeling by attempting to rotate fan and clutch assembly by hand five times. If no drag is felt, replace clutch.

FAN BLADE INSPECTION
Place fan on flat surface with leading edge facing down. If there is a clearance between fan blade touching surface and opposite blade of more than .090 inch (2 mm), replace fan. (See caution at beginning of chapter.)

Fig. 2 Variable speed fan with flat bimetallic thermostatic spring:

FAN SERVICE
To prevent silicone fluid from draining into fan drive bearing, do not store or place drive unit on bench with rear of shaft pointing downward.
The removal procedure for either type of fan clutch assembly is generally the same. Merely unfasten the unit from the water pump and remove the assembly from vehicle.
The type of unit shown in Fig. 2, may be partially disassembled for inspection and cleaning. Remove capscrews that hold the assembly together and separate the fan from the drive clutch. Next, remove metal strip on front of clutch assembly by pushing one end of it toward the fan clutch body so it clears the retaining bracket. Push the strip to the side so that its opposite end will spring out of place. Now remove the small control piston underneath it.
Check the piston for free movement of the coupling device. If piston sticks, clean it with emery cloth. If the bimetal strip is damaged, replace the entire unit. These strips are not interchangeable.
When reassembling, install the control piston so that the projection on the end of it will contact the metal strip. Next install metal strip with any identification number or letters facing the clutch. After reassembly, clean the clutch drive assembly with a cloth soaked in a suitable solvent. Avoid dipping the clutch assembly in any type liquid. Install the assembly in the reverse order of removal.
The coil spring type fan clutch cannot be disassembled, serviced or repaired. If it does not function properly, it must be replaced with a new unit.