Spirit L6-258 4.2L VIN C 2-bbl (1982)
Fan Clutch: Description and Operation
Fig. 1 Typical variable-speed fan installed
Fig. 2 Variable-speed fan with flat bi-metal thermostatic spring
Fig. 3 Variable-speed fan with coiled bi-metal thermostatic spring
The fan drive clutch, is a fluid coupling containing silicone oil. Fan speed is regulated by the torque-carrying capacity of the silicone oil. The more
silicone oil in the coupling the greater the fan speed, and the less silicone oil the slower the fan speed.
Two types of fan drive clutches are in use. On one a bi-metallic strip and control piston on the front of the fluid coupling regulates the amount of silicone
oil entering the coupling. The bi-metallic strip bows outward with an increase in surrounding temperature and allows a piston to move outward. The
piston opens a valve regulating the flow of silicone oil into the coupling from a reserve chamber. The silicone oil is returned to the reserve chamber
through a bleed hole when the valve is closed.
On the other type of fan drive clutch a heat-sensitive, bi-metal spring connected to an opening plate brings about a similar result. Both units cause the fan
speed to increase with a rise in temperature and to decrease as the temperature goes down.
In some cases a Flex-Fan is used instead of a fan drive clutch. Flexible blades vary the volume of air being drawn through the radiator, automatically
increasing the pitch at low engine speeds.
