Fan Clutches FAQs
Question No. 1
"How does a thermal clutch fan work?"
A thermal clutch fan operates using silicon fluid as a viscous coupling medium. When the clutch is cool and disengaged, most of the silicon fluid is stored in the reservoir allowing your fan clutch to slip relative to your water pump shaft thereby spinning at a lower RPM than the water pump. This saves you money because the horsepower from your engine is not wasted driving a clutch fan when it's not needed. As your engine heats up, the thermal spring on the front of the clutch expands, which opens a valve allowing the silicon fluid to drive your clutch at an increased RPM. This provides more air flow through your radiator, preventing your car from overheating.
Question No. 2
"What is the difference between a thermal and non-thermal fan clutch?"
A non-thermal fan clutch is nothing more than a thermal fan clutch always partly engaged. It provides adequate cooling when needed, however, it does not save you money by disengaging (operating at a lower RPM) when additional cooling is not needed.
Question No. 3
"At what temperature does a clutch fan engage?"
The engagement temperature varies model to model. Most automotive clutches engage between 70°C and 80°C air temperature at the face of the clutch.
Question No. 4
"How do I know if my fan clutch needs to be replaced?"
These are the most common symptoms of a failed fan clutch:
- Engine overheating – with engine hot and ignition off, spin fan 1-11/2 revolutions indicates a worn clutch.
- Excessive Fan Clutch play – push the tip of the fan blade in and out. Any visible looseness in the clutch shaft means the bearing is worn.
- Greasy build up – Oily streaks radiating outward from the hub shaft or fluid leaking at centre of thermostat spring.
- Bad bearing - Seized, turns rough or has excessive play (more than 1/4" at fan tip).
- Freezing up – If the fan blade cannot be rotated by hand, or if hand rotation causes a harsh rumbling, the fan clutch bearing has failed.
- Shaft vibration – The fan clutch is mounted on the water pump between the water pump shaft and the fan. Any vibration can mean a worn bearing in the water pump o fan clutch. Since the fan clutch and water pump have about the same life span, it makes sense to replace both at the same time.
- 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 speedor excessive high side pressures.
- Doesn't engage - Fan speed does not increase or "lock up" when the engine is hot.
- Does not disengage - Fan clutch won't slow down when the engine is cold.
Note; The fan clutch should be checked for possible replacement when a replacement water pump is being installed.
Question No. 5
"What is the difference between a standard, heavy and severe duty fan clutch?"
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 application for which they are catalogued. Standard Duty Thermal Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch fans. (1-1/2' of pitch) Flat plate impeller design with 30sq.in. of working area. 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 47sq.in. of working area allows higher operating RPM. 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.
"My fan clutch makes a loud noise when started cold. Is this normal?"
Yes, most fan clutches allow the fluid to drain into the working area when shut down and engage the clutch. At starts it may take 1-2 minutes for the clutch to slow down.