Thermostatic Fans

NOTE: Cooling system must be in good condition before performing test to prevent excessively high coolant temperature condition.

Drill a 1/8 INCH (3.18 mm) hole in top center of fan shroud. Insert a dial thermometer with an 8 INCH stem through hole in shroud. Ensure there is adequate clearance from fan blades.
Connect a tachometer and an ignition timing light (to be used as a strobe light). Block airflow through radiator by securing a sheet of plastic in front of radiator or air conditioner condenser.
Ensure air conditioner is turned off (if equipped). Start engine and operate at 2400 RPM with timing light aimed at fan blades. Within 10 minutes, air temperature on dial thermometer should read 190°F (88°C).
Fan drive should engage before or at 190°F (88°C). Fan drive engagement can be distinguished by definite increase in fan drive airflow noise. Increase in fan speed can also be determined by timing light.
When air temperature reaches 190°F (88°C), remove plastic sheet. Air temperature should drop 20°F (11°C) or more, and a definite decrease of audible fan airflow noise should be noticed. Replace fan drive if it does not function as described.
If noise or roughness can be felt when turning fan by hand, shaft seal is leaking fluid, or fan drive is frozen. Replace fan drive.