Fan and Hub

• The fan and hub consists of a central hub from which multiple fan blades are connected, and designed to rotate in a circular motion, driven by a pulley off the engine. The fan blades have an angled pitch, much like an airplane propeller, designed to draw air through a radiator for the purpose of cooling the temperature of the radiator water. Fans and hubs come in metal or light-weight plastic construction, with the plastic versions being the most popular.
  
  

Fan Clutch

• The fan clutch couples with the fan and hub assembly, and is secured by nuts or bolts. The clutch couples with the fan to engage it fully for constant spin or to disengage it fully or partially to save rotational energy. The cylindrical clutch body holds a viscous silicone oil, which is designed to move freely inside the clutch body when activated by an internal valve.
  
  

Thermostatic Spring and Valve

• The fan clutch houses a temperature-sensitive spring that opens and closes according to the tension applied to the spring. The spring has a circular, coil-like construction and is permanently fixed to the inside or underside of the clutch body. A valve sits inside the clutch, connected to one end of the thermostatic spring. The valve opens and closes, allowing a certain amount of oil to pass through it, or closes slightly to restrict the volume of oil that moves.
  
  

Pulley and Belt

• A round pulley, usually made of metal and grooved to fit a fan belt, attaches to the clutch body. A fan belt, either serpentine or V-groove, drives the pulley to provide the spinning rotation of the fan and hub. The fan and belt provide the primary energy to turn the fan hub assembly.
  
  

Combined Component Operation

• When the engine compartment becomes hot enough, the heat expands the thermostatic spring, which opens up the interior valve. Once the valve opens, oil flows through it to the clutch. The clutch engages with the fan hub to turn it. When the fan has cooled the engine sufficiently, the thermostatic spring begins to close, partially disengaging the clutch from the fan. The fan will spin at half speed during cooling. When the engine has cooled sufficiently, the thermostatic spring will close completely, cutting off the flow of oil. This disengages the clutch from the fan.
  
  

Fan Hub Assembly Advantages

• A fan hub assembly has a unique characteristic in that it works only when needed. The fan will spin at top speed to cool a hot engine, and it will reduce its speed when the engine begins to cool. As a result, excess drag becomes eliminated, saving horsepower energy, which saves fuel. Fan hub assemblies aid in cold engine warm-up by keeping the fan static until operating temperature has been reached. Fan hub assemblies offer much quieter operation, and typically do not vibrate like the older fixed fans.