Question: My engine has an electric cooling fan. But
the fan doesn't run all the time. Is that normal?
Answer:Yes. The cooling fan is only needed when engine
temperature rises above a predetermined level -- or when there
is an increased load placed on the cooling system (as when running
your air conditioner). The rest of the time, running the fan
would be a waste of electrical energy so it is turned off.
Electric cooling fans are found on most front-wheel drive
vehicles with transverse mounted engines as well as many late
model rear-wheel drive vehicles. Electric fans are used on FWD
cars because the fan doesn't require a belt drive and can be mounted
independent of the engine's location. What's more, electric fans
require less power to operate (for improved fuel economy and performance),
they're quieter, and they allow more precise control over cooling.
By comparison, a mechanical belt-driven fan can require anywhere
from 5 to 15 horsepower depending on engine speed and the size
of the fan. Even with a fan clutch to reduce the drag at higher
speeds, it's still a lot of wasted power.
FAN OPERATION
At highway speeds, there is usually enough airflow through
the radiator that a fan isn't needed. So the fan usually only
operates when the vehicle is sitting in traffic or driving at
slower speeds.
On older applications, the electric fan is controlled by a
temperature switch located in the radiator or engine. When the
temperature of the coolant exceeds the switch's rating (typically
195 to 235 degrees F), the switch closes and energizes a relay
that supplies voltage to run the fan. The fan then continues
to run until the coolant temperature drops back below the opening
point of the switch. Most electric fans are also wired to come
on when the A/C is on. Many vehicles also have a separate fan
for the A/C condenser (dual fan systems). One or both fans come
on when the A/C is on.
In newer vehicles with computerized engine controls, fan operation
is regulated by the engine control module. Input from the coolant
sensor, and in many cases the vehicle speed sensor too, is used
to determine when the fan needs to be on.
CAUTION: Many electric fans are wired to come on anytime
the engine is above a certain temperature, regardless of whether
the engine is running or not. This means the fan may come on
after the engine has been shut off. So keep your fingers away
from the fan at all times unless the battery or fan motor wires
have been disconnected.
CHECKING THE FAN
Four things can prevent a fan from coming on when it should:
a bad temperature switch or coolant sensor (or problem in the
switch or sensor wiring circuit); a bad fan relay; a wiring problem
(blown fuse, loose or corroded connector, shorts, opens, etc.);
or a failure of the fan motor itself. Only the latter would require
replacing the fan motor.
One way to check the operation of the fan motor is to jump
it directly to the battery. If it spins, the motor is good, and
the problem is elsewhere in the wiring or control circuit. Another
check is to test for voltage with a voltmeter or test light at
the fan's wiring connector. There should be voltage when the
engine is hot and when the A/C is on.
