Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
Fan Clutch: Description and Operation
Fig. 1 Fan drive clutch assembly, 1984---87. 1980---83 similar
Fig. 2 Variable speed fan with flat bimetallic thermostatic spring
Variable Speed Fan W/Bi-Metallic Coiled Thermostatic Spring
The fan drive clutch, Fig. 1, 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.
There are two types of fan drive clutches in use, one with a flat bimetallic thermostatic spring, Fig. 2, and the second with a coiled bimetallic
thermostatic spring, Fig. 3.
The fan drive clutch with the flat bimetallic spring works with a control piston on front of the fluid coupling to regulate the amount of silicone oil
entering the coupling. The bimetallic strip bows outward with an increase in ambient temperature and allows a piston to move outward. This 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.
The second fan drive clutch uses a heat-sensitive, coiled bimetallic spring connected to an opening plate which brings about similar results. Both units
cause the fan speed to increase with a rise in temperature and to decrease as temperature decreases.
