Electric Fan & Fan Clutch

Electric fan is standard on the 7.4L with air conditioning. Verify that the electric fan is operating properly. The fan should engage at approximately 225 degrees F. Also verify that the fan is turning in the right direction. When viewed through the grille, the fan should be turning counter-clockwise.

FAN


Check the fan for damaged blades. Bent or missing blades can cause poor cooling system performance as well as vibrations. Verify that the fan is correct for the engine and application. See the service parts book (Group 1.064) for correct usage.

FAN CLUTCH


Verify that the fan clutch is correct for the engine and application. The clutch has a two letter code stamped on the housing, usually on or near the outside edge. The service parts book (Group 1.050) references the codes in relation to the service part numbers and application.

DIAGNOSIS

With the engine off, rotate the fan by hand, It should have some drag, but it should turn smoothly. If it does not turn smoothly, does not turn at all or exhibits extreme bearing looseness, it should be replaced.

When the engine has been off for a considerable period of time. (greater than eight hours), the fan clutch may be engaged when the engine is first started. The clutch will remain engaged until the silicone fluid inside can be redistributed to its normal disengaged operating condition. The fan clutch should disengage after not more than five minutes if the engine speed is kept about 2,000 RPM. A reduction in fan noise will be noticeable when the fan clutch disengages.


To verify the engagement and disengagement of the fan clutch in relation to engine temperature, connect a scan tool to the vehicles ALDL Connector and observe the engine coolant temperature. Coolant temperature should be below 140 degrees F before the start of the test. Start the engine, let idle and observe the coolant temperature. The temperature should rise at a steady rate until the thermostat opens (about 195 degrees F). When the thermostat opens, the coolant temperature may momentarily drop a few degrees, or stay constant for a minute of two. This should be considered as normal. At this point it will be necessary to road test the vehicle in order to get an appropriate amount of air flow across the radiator.


Drive the vehicle at a steady speed and continue to monitor coolant temperature until approximately 203-205 degrees F is obtained. At this temperature you should be able to hear an increase in fan noise as the clutch engages. If the fan clutch does not engage, continue driving and monitoring the coolant temperature until 210 degrees F is obtained. If the fan clutch has still not engaged, the clutch should be replaced.


NOTE: If the ambient temperature during the road test is less than 70 degrees F, it may not be possible to obtain the coolant temperature of 203-205 degrees F required for the clutch test. If this condition is encountered, it may be necessary to partially obstruct (about 50%) the air flow across the radiator or A/C condenser with a piece of cardboard. Remove the cardboard upon completion of the clutch test.


When the fan clutch engages, the engine coolant temperature will decrease until a temperature of approximately 195 degrees F. At this point the fan clutch should disengage resulting in a decrease in fan noise. If the fan clutch does not disengage, continue driving and monitoring coolant temperature until 190 degrees F is reached. If the fan clutch has still not disengaged, the clutch should be replaced.