Cooling fans are driven by the engine’s crankshaft or by an electric motor. They provide air flow through the radiator fins, transferring heat from the engine’s coolant to the outside air. The radiator will not operate effectively without proper air flow. This air flow is vital, especially while idling or traveling slowly. Today’s aerodynamic designs have reduced the size of the radiator grill demanding even more air flow from electric radiator cooling fans.
Many longitudinal engines have a fan attached to the water pump flange. These fans often have a fan clutch to control air flow. Bent or missing blades on any fan will cause an imbalance and severe vibration. This can result in damage to the water pumps bearings and seals. Check for cracks and excessive wear in belts and fan blades as part of an initial inspection.
Viscous Fans: Viscous fan clutches are driven by the engine’s crankshaft. The typical viscous fan clutch contains silicon oil that may leak from the unit. This thick fluid's viscosity is measured in CST’s or centistokes. Check the unit for fluid leaks through the seams and around the shaft. They also have a thermostatic spring that should be inspected. It can be checked be releasing it from its seat and measuring the distance between the spring and its retainer. Always check for manufacturer’s specifications and special procedures.
Electric Fans: Electric fan blades are typically made of plastic. They wear and begin to crack, that's why they should be carefully inspected for wear. They’re controlled by the PCM; it uses the signal from the ECT or engine coolant temperature sensor. This sensor senses the temperature of the engine’s coolant and sends a variable voltage signal to the PCM. The PCM operates the fan motor through the engine’s cooling fan relay.