FAQ - Fan Clutches

How do I know if my fan clutch needs to be replaced?

Answer: A malfunctioning fan clutch can be hard to diagnose. Typically, the vehicle will NOT overheat unless operating in severe duty conditions. Since the vehicle is not overheating, the technician is not inclined to suspect an airflow problem. The challenge is to determine if the fan clutch is engaged and close to engine rpm. With an inexpensive infrared tachometer, a bad viscous fan clutch is much easier to diagnose by comparing fan speed to shaft speed. An engaged fan clutch will approximately read 80-90% of shaft speed. A disengaged fan clutch will approximately read 20-30% of shaft speed. A scan tool should also be used to check for codes that have been set by the EVC.

These are the most common symptoms of a failed fan clutch:

• Leaking fluid - Oily build up around the bearing or thermal spring
• Bad bearing - Seized, turns rough or has excessive play (more than 1/4" at fan tip)
• Worn thermal spring - Spring is loose

Some fan clutches will show no visible indication of a problem yet may still be faulty. The following may also indicate a faulty fan clutch:

• Fan spins excessively - Three or more times when hot engine is shut off
• Poor air conditioning - At low speed or excessive high side pressures
• Doesn't engage - Fan speed does not increase or "locks up" when the engine is hot
• Does not disengage - Fan clutch won't slow down when the engine is cold

What is the difference between a standard, heavy and severe duty fan clutch?

Answer:  Each fan clutch type is designed to simulate the performance of the original equipment clutch that it replaces. All fan clutches are for specific applications and should be applied only on the vehicle for which they are cataloged. Use of the incorrect fan clutch may result in poor cooling, excessive noise, reduced fuel economy or fan clutch failure.

• Standard Duty Thermal: Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch (1-1/2" of pitch). Flat plate impeller design with 30 sq. in. of working surface. 

• Heavy-Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans (2 1/2" of pitch). Land and groove design with 47 sq. in. of working area allows higher operating RPM's. 

• Severe Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 sq. in. of working area. Larger working surface provides cooler running and longer life expectancy.

At what temperatures do fan clutches engage?

Answer:  Most fan clutches engage at about 170°F air temperature (about 180-190°F engine temperature). They reduce the temperature about 20°F before disengaging.