How does a thermal clutch fan work?

A thermal clutch fan operates using silicon fluid as a viscous coupling medium. When the clutch is cool and disengaged, most of the silicon fluid is stored in the reservoir allowing your fan clutch to slip relative to your water pump shaft thereby spinning at a lower RPM than the water pump. This saves you money because the horsepower from your engine is not wasted driving a clutch fan when it's not needed. As your engine heats up, the thermal spring on the front of the clutch expands, which opens a valve allowing the silicon fluid to drive your clutch at an increased RPM. This provides more air flow through your radiator, preventing your car from overheating.
A thermal clutch fan operates using silicon fluid as a viscous coupling medium. When the clutch is cool and disengaged, most of the silicon fluid is stored in the reservoir allowing your fan clutch to slip relative to your water pump shaft thereby spinning at a lower RPM than the water pump. This saves you money because the horsepower from your engine is not wasted driving a clutch fan when it's not needed. As your engine heats up, the thermal spring on the front of the clutch expands, which opens a valve allowing the silicon fluid to drive your clutch at an increased RPM. This provides more air flow through your radiator, preventing your car from overheating.