Description & Operation

Thermal viscous fan drive a is coupling used to connect the fan blades to the water pump shaft through a union nut. Union nut is right hand threaded. Viscous fan coupling allows 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. Until additional engine cooling is necessary fan will remain at a reduced RPM regardless of engine speed.

When sufficient heat is present, will the viscous fan drive engage. Air flow through the radiator core causes viscous fan drive to lock-up which increases fan speed providing additional engine cooling. Once the engine has cooled, the coolant temperature will drop. Viscous fan drive again reacts and fan speed is reduced to disengaged speed.