Figure 6-9.Variable pitch fan.
speed is controlled by the torque-carrying capacity of
the oil. The more oil in the coupling, the greater the fan
speed; the less oil in the coupling, the slower the fan
The thermostatic fan clutch has a temperature
sensitive, bimetallic spring that controls fan action. The
spring controls oil flow in the fan clutch When cold,
the spring causes the clutch to slip, speeding engine
warm-up. After reaching operating temperature, the
spring locks the clutch, providing forced air circulation.
An electric engine fan uses an electric motor and a
thermostatic switch to provide cooling action (fig.
6-10). An electric fan is used on front-wheel drive
vehicles having transverse mounted engines. The water
pump is normally located away from the radiator.
The fan motor is a small, direct current (dc) motor.
It mounts on a bracket secured to the radiator. A metal
or plastic fan blade mounts on the end of the motor shaft.
A fan switch or temperature-sensing switch
controls fan motor operation. When the engine is cold,
the switch is open, keeping the fan from spinning, and
speeds engine warm-up.
When coolant temperature
reaches approximately 210°F, the switch closes to
operate the fan and provide cooling.
An electric engine fan saves energy and increases
cooling system efficiency. It only functions when
needed. By speeding engine warm-up, it reduces
emissions and fuel consumption. In cold weather, the
electric fan may shut off at highway speeds. There may
be enough cool air rushing through the grille of the
vehicle to provide adequate cooling. On some models a
timed relay may be incorporated that allows the fan to
run for a short time after engine shutdown. This, in
conjunction with thermosiphon action, helps to prevent
boilover after engine shutdown.
Figure 6-10.Electrically motorized fan.