Fan Clutch: Testing and Inspection

Fig. 4 Disconnecting bi-metal spring:

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 bi-metal spring type, it may be tested while the vehicle is being driven. To check, disconnect the bi-metal spring, Fig. 4, and rotate 90 degrees 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.