Scott wrote:
>Fan clutches have been around since long before the Magnum engine. And
>they're all belt driven, the clutch just allows the fan to free wheel when
>it's not needed, reducing drag on the engine. (Although an electric fan is
>even less mechanical drag, they don't pull as much air as a fan clutch
>arrangment.) If the fan clutch goes bad, it'll freewheel when it's not
>supposed to, and not pull the air through the radiator. If the thermostat is
>stuck shut, the temp would continue to climb when you're moving, since
engine
>rpm goes up. If it's stuck open, the engine will take longer to warm up, but
>it will run at about normal temperature.
>Unless I'm overlooking something really obvious... :)
>Scott
>'94 318
><A HREF="http://members.aol.com/McKennaRacing/">McKennaRacing.com</A>
Good point Scott. For those that are not familiar with fan clutches and
their location I will try my best to describe them and their location _In
general_, as in not vehicle specific. They look like a large aluminum
heatsink and are located in the center of the cooling fan. The fan is
bolted to the clutch and the clutch is bolted to the water pump or whatever
and is driven by the belt system. In layman's terms: It's the large light
grey metal thingy in front of the radiator fan.
A real quick way to check the condition of the clutch is to grab hold of
the radiator fan (with the engine off (one of those "duh" statements)), and
give the fan a quick spin in the normal fan rotation direction. If the fan
quickly stops, the clutch is in working condition (theoretically). If the
fan continues to spin and takes it's time to stop, the clutch is bad. Even
with a brand new clutch, the fan will move, but there will be resistance to
movement. That resistance is caused by a silicone fluid inside the
clutch. That fluid couples the clutch to the fan. When the engine is off
or idling, the fluid is near the center of the clutch which couples the
clutch to the fan, when the engine speed increased, centrifugal force
causes the fluid to flow to the outside edges of the clutch transferring
less torque to the fan and causes it to slow, but not stop.
There are two types of fan clutches - thermal and non-thermal. Thermal
types have a small bi-metallic coil on the front of the clutch which faces
the radiator. It is a temperature sensor that will cause the fan clutch to
engage only when the temperature of the air coming through the radiator
reaches a certain degree. So the fan is capable of free spinning at idle
and low speeds when cold, but engages the fan at the set temperature. The
fan will still disengage at higher speeds, usually at 1500 RPM or so. The
non-thermal is like the one I described at the beginning of this book -
engages at low speeds, free spins at high engine speeds.
Thought it would help to describe and explain the fan clutch for those that
aren't too familiar with it.
Mike
'99 RC 4x2 V6 5spd
__________________________
mschwall@flash.net
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:46:37 EDT