Emery is mostly correct. The OEM fan clutch was made by Eaton Corp, where I was
employed for 23 yrs. The only exception I'll take to his comment is that a
silicone fluid clutch will never lock up. In fact the fan speed will peak out at
a predetermined speed and stay pretty constant regardless of the input (water
pump) speed. Of course as the slip speed increases, more heat is built up and
the internal temperature rises and actually drops the fan speed a bit.
Also, there was some discussion about how to store the fan clutch off the
engine. The best orientation is nose down, but you need to be careful not to
damage the bimetalic coil at the front of the unit. If you store the unit shaft
flange down, the silicone fluid will seep into the ball bearing and dilute its
grease and eventually leak through the seals. Storing the unit with shaft
horizontal would be fine, but it's a little awkward. Unless you lose some of the
silicone fluid, the orientation of storing should have no detrimental effect on
the unit's performance.
By the way, the most common failure mode is bearing failure. There's a sealed
single row ball bearing with a special, high temp grease. After a lot of use,
the grease tends to dry out and then the bearing bites the dust.
The roar sound on start-up means it's working. Typically, the silicone fluid
drains down inside the unit while it's standing still. There is a simple pumping
mechanism inside that pushes the silicone fluid into the reservoir (front) when
cooling is not needed. As that happens the fan speed goes down to an idle
condition of around 500 RPM, even when the water pump is turning at high RPM. As
Emery said, when the radiator heats the air to a high enough temperature to
activate the bimetalic coil, a valve slides open to allow the fluid to fill a set
of concentric, close fitting grooves between a disk that's attached to the input
shaft and the "body" that the fan is attached to. The grade or viscosity of the
silicone fluid determines how much torque it will transmit and therefore the
speed of the fan. An ingeniously simple but effective device.
Someone mentioned hearing the fan come on when entering a freeway ramp. It also
happens frequently when the engine idles for a while. Basically when there isn't
much air flowing through the radiator, the temperature at the bimetalic coil goes
up and engages the fan. Then when you start moving, the temperature returns to
normal and the fan cuts back out. After that it should come on and go off based
on ambient temperature and engine load.
Clark Searle
78 Kingsley
Mt. Pleasant, MI
> I have not replaced with the Hayden one but the rest have a coil spring that
> can be rotated to a position that the clutch is locked up and never cuts out.
> Remove the clutch and check to see if your has this spring. If so, try
> rotating the spring and see if that helps. The clutch works by temperature
> opening a valve that allows silicone fluid to flow from the reservoir to the
> clutch body. The more silicone, the more the clutch will grip. At a high
> enough temperature it will fully lock up. As it cools the valve closed and
> the silicone returns to the reservoir.
>
> Emery Stora
> 77 Kingsley
> Santa Fe, NM
