Engine Cooling Fan: Description
The flex-blade fan assembly is designed to allow blades to flex as engine RPM increases. Blade pitch decreases as RPM increases, thereby saving power and decreasing noise level. Keep fan belt adjusted to proper tension as necessary. See Fig 1.
Many air conditioned models use a thermostatically controlled fluid fan and torque control clutch. Thermal control drive is a silicone-filled coupling connecting fan to a fan pulley, and is operated by an internal control valve. The control valve is operated by a temperature sensitive bimetallic coil (or strip) and controls flow of silicone through the clutch. See Fig 2.
During periods of operation when radiator discharge air temperature is low, fan clutch speeds are slowed, decreasing fan speed and increasing engine warm-up. High radiator discharge air temperature causes bimetallic coil or strip to allow a greater flow of silicone to enter clutch. This increases drag between driven member and driving member, resulting in a higher fan speed and increased cooling.