Thermal Fan Clutch Test

[bugeye01]

I have a 1995 F350 with 460. I had the truck in a repair shop recently and one of the mechanics commented that it looks like my fan clutch is bad. So my question is, How do you test the thermal fan clutch?

 

[blacksnapon]

Fan Clutch Test
Spin the fan. A light resistance should be felt. If there is no resistance or very high resistance, the minimum and maximum fan speeds must be checked as follows:


Disengaged Fan Clutch Requirement Test — Cold

WARNING: TO AVOID THE POSSIBILITY OF PERSONAL INJURY OR DAMAGE TO THE VEHICLE, DO NOT OPERATE THE ENGINE (6007) UNTIL THE FAN HAS BEEN FIRST EXAMINED FOR POSSIBLE CRACKS AND SEPARATION.

Using a suitable marker, mark the water pump pulley (8509), one of the fan blade retaining bolts and the crankshaft pulley (6312).
Connect a tachometer to the engine.
Install a throttle adjusting tool.
Connect a Sun Strobe Light or equivalent. This can be an SLT-1 or SLT-2 Strobotach or an STA-1 Strobe Trigger adapter for the Sun Distributor Test Stand. A Rotunda Digital Photoelectric Tachometer 055-00108 or equivalent may also be used for this test.
Start the engine and run it at approximately 1500 rpm until engine temperature has normalized.
Adjust the engine to the testing speed in the Specifications at the end of this section.
Operate the strobe light at water pump test speed and aim it at the water pump pulley. Adjust the engine speed until the light flashes and the water pump pulley marks are synchronized.
Aim the timing light at the fan retaining bolts. Adjust the strobe light until it is synchronized with the marked fan retaining bolt (fan appears to stand still).
The fan speed must not be greater than the specified fan test speed at water pump test speed.
Turn the engine OFF.
If the fan speed was greater than the specified fan test speed, check for proper parts usage.
If the correct parts are used, replace the fan clutch (8A616).

If the part(s) are not the correct ones, replace the part(s) and perform the test again.

If the engaged fan clutch requirement test is going to be performed, do not remove the tachometer, strobe light or throttle adjusting tool.
If a Engaged Speed Fan Clutch Requirement test is not going to be performed, remove the tachometer, strobe light and throttle adjusting tool.
Maximum Speed Fan Clutch Requirement Test

WARNING: TO AVOID THE POSSIBILITY OF PERSONAL INJURY OR DAMAGE TO THE VEHICLE, DO NOT OPERATE THE ENGINE WITH THE HOOD OPEN UNTIL THE FAN HAS BEEN FIRST EXAMINED FOR POSSIBLE CRACKS AND SEPARATION.

If the disengaged fan clutch requirement test was not performed, follow Steps 1 through 5 under Disengaged Fan Clutch Requirement test.
Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille (8200), this will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.
Place the air conditioning selector, if so equipped, in the maximum position and the blower switch in the high position.
Adjust the strobe light to water pump test speed.
Start the engine and adjust it until the water pump pulley is synchronized with the strobe light. This will be near the engine testing speed given in Specifications.
Synchronize the timing light with the fan to fan clutch retaining bolt.
The fan speed must meet or exceed the specified minimum fan blade test speed at water pump test speed.
If the fan speed was less than the specified fan test speed, replace the fan clutch.

 

[bugeye01]

Thanks! I appreciate your help. I should have done a little Internet search first. I did a search just after I made the post and found a page with almost the same recommendation, plus a description of how the thermal fan clutch works. I read on that page that the silicon-based oil deteriorates which causes maximum fan speed to drop about 200 rpm/year, so I figured I should probably replace the 17-year old clutch anyway.