Radiator Cooling Fans
Radiator cooling fans can be driven by the crankshaft or by an electric motor. They provide airflow through the radiator fins, transferring heat from the engine's coolant to the outside air. Some vehicles have a fan installed in front of the condenser to assist in heat exchange. Both the radiator and the condenser require airflow to exchange heat to the atmosphere. This airflow is vital, especially idling, while the vehicle is sitting still and not creating ram air.
When the fan is mounted to the water pump flange, bent or missing blades will cause an imbalance, resulting in damage to the water pump's bearings and seals. Always check for cracks and excessive wear in today's plastic fan blades.
Viscous Fans: The crankshaft drives a viscous fan clutch. The typical viscous fan clutch contains silicon oil that can leak from the unit. The viscosity of this thick fluid is measured in CST or centistokes and wears over time. Check the unit for leaks through the seams and around the shaft. A stuck/frozen fan clutch makes a whirling sound that increases with engine speed. Check the accessory belt for wear and glazing.
They also have a thermostatic spring. Check it by releasing it from its seat and measuring the distance between the spring and its retainer. Always check the manufacturer's specifications for special procedures.
Electric Fans: Electric fan blades are typically made of plastic and should be inspected for cracks and wear. They're controlled by the ECM and an (ECT) or engine coolant temperature sensor that senses the temperature of the engine's coolant. The PCM monitors a variable voltage signal. It then compares this signal to its internal memory; if the coolant is hot enough, the PCM sends a low current voltage signal to the fan relay. The relay contacts close and complete the fan motor's circuit, activating the fan motor.