Discovery I (LJ) V8-4.0L (1996)
Viscous unit slipping (Engine at normal running temperature)
1. Inner member (drive in fast)
2. Outer member (drive out slow)
3. Running clearance
4. Valve plate
5. Valve (closed)
6. Bi-metal
7. Fluid seals
8. Ball race
9. Fluid chamber
10. Fluid chamber
If the engine speed is increased the degree of slip will also increase to limit the maximum fan speed.
Hot conditions
When operating in high ambient temperatures or when stationary in traffic, the bi-metal thermostat will operate and open the valve port between
chambers A and B. Opening the valve (see illustration below) allows the fluid to circulate between the two members, causing the unit to couple, thus
increasing the fan speed and cooling effect.