What is a Fan Clutch?

Your car’s engine generates a substantial amount of heat which requires the assistance of engine cooling fans. While the vehicle is in motion at a lower speed or at an idle, an engine cooling fan draws air through the radiator. The fan clutch is one of the most essential components in the operation of cooling fans and greatly contributes to the overall operation of the engine. While many new vehicles use electric cooling fans, many older vehicles utilize a mechanical fan clutch to help control the fans.

The fan clutch is a thermostatic device, operating based on temperature, that is most often mounted to the fan and on the water pump or other belt-driven pulley. The fan clutch spins loosely until the temperature in the engine reaches a specific level of heat, engaging the clutch and simultaneously allowing the fan to perform efficiently. When the engine is cool or functioning at a normal operating temperature, the fan disengages or slows to a required speed to assist in regulating the engine temperature.  

Vehicles are often equipped with three distinctive types of engine cooling fans such as flex, clutch, and electric. While each fan type has it’s distinctive “pros and cons” let’s explore the difference between flex and clutch fans:

Flex Fans

Flex fans are equipped with a steel frame and blades made from plastic, steel, or other flexible materials. They’re designed to flatten out at a specified RPM when not needed, to assist in cooling the engine and alleviate power-reducing drag on the engine. The flex fans possess the ability to pull air through the radiator during an idle and flatten out. This is similar to a clutch fan slipping to maintain the proper engine temperature. While flex fans assist with idle or slow speed operations, they have been known to be noisy at low RPMs and deprive the engine of more horsepower than other varieties of fans available..

Clutch Fans

Clutch fans are available via two operations: thermal and non-thermal. Thermal Fan Clutches, however, are the most efficient form of engine driven fans. A bi-metal thermal spring is located on the front of the fan that expands or contracts based on heat from the air passing through the radiator. When the temperature reaches around 170 degrees Fahrenheit, the spring expands and releases a chamber allowing silicone to flow to the clutch. The clutch is then engaged and turns at about 70 to 90 percent of the speed of the water pump, usually during slower speeds or at idle. As the vehicle begins to speed up, a substantial amount of air passes through the radiator to cool it down. The sheer volume of air cools the bi-metal thermal spring, triggering it to disengage. At this moment, the fan is turning nearly 20 percent of the speed of the water pump since the fan isn’t needed, as more air rushes through the radiator. The reduction in drag as it cruises helps to increase fuel economy by increasing horsepower.

The Non-Thermal Fan Clutch is a more economical alternative in comparison to a thermal fan clutch, as they are continuously engaged and turn at 30 to 60 percent of the water pump shaft speed. While the non-thermal fan clutch is a lower cost option, they require more power to operate, don’t last as long as thermal clutches, and are less effective at cooling during low speeds, resulting in a reduction in fuel economy.

Symptoms of Trouble

One of the first indications that the clutch fan is failing, or has failed, is quite obvious. The engine may run hotter at lower speeds and at idle and the air conditioning performance drops. Here are some other signs your fan clutch needs to be replaced:

    • Noisy Fan Clutch – A scraping or squealing sound that ceases when you turn the A/C fan off.
    • Loud Engine Sound – The engine will produce this sound due to the fan blowing at full speed, caused by the fan clutch stuck in the engaged position.
    • Overheating – Overheating or higher temperatures than normal.
    • Reduction in performance – A significant and obvious drop in power, acceleration, and fuel economy.

If you notice your vehicle exhibiting any of the symptoms above, don’t wait to have a trusted mechanic inspect the vehicle’s cooling system, specifically the cooling fan and cooling fan clutch. A dysfunctional component within the cooling system could lead to overheating, which can result in more serious issues or damage to the engine, if left unattended. Ensuring your engine keeps cool, will keep you on the road longer.