Viscous fan operation (Cooling system - Td5) (page 2 of 2)

As the coolant temperature increases, the heat emitted from the radiator causes the bi-metallic coil to tighten. This movement of the coil moves the valve to which it is attached. The rotation of the valve exposes ports in the valve plate which allow the silicone fluid to spill into the fluid chamber. As the fluid flows into the clearance between the annular grooves in the drive plate and body, drag is created between the two components. The drag is due to the viscosity and shear qualities of the silicone fluid and causes the drive plate to rotate the body and fan blades.

As the coolant temperature decreases, the bi-metallic coil expands, rotating the valve and closing off the ports in the valve plate. When the valve is closed, centrifugal force pushes the silicone fluid through the return port, emptying the fluid chamber. As the fluid chamber empties, the drag between the drive plate and the body is reduced and the body slips on the drive plate, slowing the rotational speed of the fan.