A fan clutch disengages the cooling fan as engine speed increases, saving power and increasing fuel consumption. Prior to the 1970s, American-made automobiles used a direct-drive fan that robbed the engine of power at highway speeds. A thermostatically controlled fan clutch is operated by a fluid coupling and a bad fan clutch can cause the engine to overheat or the air conditioner to not cool properly. Periodic checks should be performed on the cooling fan to ensure that it is working properly.
A fan clutch is a device found in a car’s cooling fan. In most cases, the fan is attached to the fan clutch by four bolts. As engine speed increases, the fan clutch disengages and puts the fan in a freewheel mode. With the fan clutch in this mode, the engine does not rotate the fan clutch, which saves power and increases fuel consumption. Some types of fan clutches are operated by a thermostat and only engage when the engine reaches a specific temperature.
Prior to the 1970s, American-made automobiles used a direct-drive fan that rotated continuously at engine speed. This type of fan cools the engine well at low speeds or idling in heavy traffic, but the fan actually robbed the engine of power at highway speeds. Air and wind coming through the vehicle’s radiator caught the fan blades and slowed them down. This action caused the engine to overrun the fan, requiring the driver of the vehicle to accelerate more to maintain engine speed.
The thermostatically controlled fan clutch is operated by a fluid coupling. When the engine temperature rises, the coupling engages. The most common sign of a fan clutch failure is an engine that gets too hot or overheats while sitting in traffic; With this type of fault, the fan does not come on when the engine gets hotter. In cold climates, a frequent sign of fan failure is a vehicle that will not reach operating temperature. In this scenario, the fan runs continuously and never allows the coolant to reach the proper temperature.
The engine fan does more than just cool the engine. In summer, the vehicle’s air conditioning system is also cooled by the engine fan. As the fan draws air through the vehicle’s radiator, it also draws air through the air conditioning condenser. When there is a bad fan clutch, it will usually not pull enough air through the condenser to properly cool the system. The result is an air conditioner that does not cool. As the vehicle accelerates, the air conditioner cools due to the airflow over the condenser.
Periodic checks should be performed on the cooling fan to ensure that it is working properly. The fan should spin with a slight resistance while the motor is not running. If the fan cannot be turned by hand while the engine is off, the clutch may require replacement. If the fan spins freely without any resistance, the fan clutch may also require replacement.
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