Cooling Fans
Cooling fans can be driven the crankshaft or by an electric motor. Fans provide air flow through the radiator fins transferring heat from the engines coolant to the outside air. The radiator will not operate effectively without proper air flow. This air flow is vital, especially while idling or when the vehicles engine is running while the vehicle is not moving fast enough to create air flow. If mounted to the water pump flange, bent or missing blades will cause an imbalance resulting in damage to the water pumps bearings and seals. Always check for cracks and excessive wear in fan blades.
Viscous Fans: These fans are driven by the crankshaft so it's important to check the belt for wear and glazing. The typical viscous fan clutch contains silicon oil that may leak from the unit. This fluids viscosity is measured in CST or centistokes and will wear over time. Check the unit for 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 manufacturers specifications or special procedures.
Flex Fans: These fans are also belt driven so carefully inspect the belt for wear and tension. They operate by changing the pitch of the blade in relation to engine speed. At higher engine speeds the pitch is decreased to reduce the power required to turn the fan. When idling at a red light the pitch will be at its maximum drawing the most air volume through the radiator.
Electric Fans: Electric fan blades are typically made of plastic and must be inspected for cracks and wear. They are operated by an ECT or engine coolant temperature sensor that senses the temperature of the coolant. A variable voltage signal is sent to the PCM. The PCM then compares this signal to its internal memory and if the coolant is hot enough sends a low current voltage signal to the fan relay. The relay then sends a high voltage signal to the fan motor.
