Viscous Fan Drive: Testing

If the fan assembly spins freely without drag (the fan blades will revolve more than five turns when spun by hand), replace the fan drive. This spin test must be performed when the engine is cool. For the following test, the cooling system must be in good condition. It also will ensure against excessively high coolant temperature.

1. Drill a 1/8" (3.18 mm) diameter hole in the top center of the fan shroud.
2. Obtain a dial thermometer with an 8" stem (or equivalent). If should have a range of 0-220°F (-18-105°C). Insert thermometer through the hole in the shroud. Be sure that there is adequate clearance from the fan blades.
3. Connect a tachometer and an engine ignition timing light (timing light is to be used as a strobe light).
4. Block the air flow through the radiator. Secure a sheet of plastic in front of the radiator (or air conditioner condenser). Use tape at the top to secure the plastic and be sure that the air flow is blocked.
WARNING: Use extreme caution when the engine is operating. DO NOT stand in n direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
5. Be sure that the air conditioner (if equipped) is turned off.
6. Start the engine and operate at 2400 RPM. With ten minutes the air temperature (indicated on the dial temperature) should be up to 190°F (88°C). Fan drive engagement should have started to occur at between 165-180°F (74-82°C). engagement is distinguishable by a definite increase in fan flow noise (roaring). The timing light also will indicate an increase in the speed of the fan.
7. When the air temperature reaches 190°F (88°C), remove the plastic sheet. Fan drive disengagement should have started to occur at between 135-175°F (57-79°C). A definite decrease of fan flow noise (roaring) should be noticed. If not, replace the defective viscous fan drive unit.