VARIATIONS
There are two basic types of cooling fans, belt-driven and electric.
- A belt-driven fan is powered by a drive belt attached to
the water pump pulley; it operates only when the engine is on. Most modern
belt-driven fans have a fluid clutch between the fan and water pump pulley. The
clutch is temperature-controlled and will slip at high speeds to prevent
unnecessary engine cooling, power loss and excess underhood noise. At cold
temperatures, the fan speed will be limited as well. Some belt-driven fans have
flexible fan blades that change position at different speeds. At low speed, the
blades have a normal shape to help pull much air through the radiator. However,
at high speed, the blades flatten out and require less power to rotate.
- An electric fan is powered by an electric motor and can
operate with the engine on or off. This is the slight whirring noise that is
heard immediately after the engine is shut off. Electric fans are usually used
on small engines to save horsepower and reduce engine drag. The fan is
activated by a temperature sensitive switch that turns on when the coolant is
hot.