RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Fan Clutch: Description and Operation
FAN DRIVE VISCOUS CLUTCH
DESCRIPTION
The thermal viscous fan drive is a silicone-fluid- filled coupling used to connect the fan blades to the water pump shaft. The coupling allows the fan to
be driven in a normal manner. This is done at low engine speeds while limiting the top speed of the fan to a predetermined maximum level at higher
engine speeds.
OPERATION
A thermostatic bimetallic spring coil is located on the front face of the viscous fan drive unit (a typical viscous unit is shown. This spring coil reacts to
the temperature of the radiator discharge air. It engages the viscous fan drive for higher fan speed if the air temperature from the radiator rises above a
certain point. Until additional engine cooling is necessary, the fan will remain at a reduced rpm regardless of engine speed.
Only when sufficient heat is present, will the viscous fan drive engage. This is when the air flowing through the radiator core causes a reaction to the
bimetallic coil. It then increases fan speed to provide the necessary additional engine cooling.
Once the engine has cooled, the radiator discharge temperature will drop. The bimetallic coil again reacts and the fan speed is reduced to the previous
disengaged speed.
