Re: [Chrysler300] Fan, Fan Clutch, Fan Shroud

[Keith Boonstra <kboonstra@xxxxxxxxxxxx>]

A fan clutch allows the fan to run at a lower RPM than the water pump 
shaft that powers it, reducing both power consumption and noise under 
the hood.  With the right pitch to the fan blades, a 70% reduction to 
the RPM still allows enough air to be pulled through the radiator to 
handle cooling in almost all circumstances.

There are two styles of fan clutches used - thermally activated and 
non-thermal.  Both function by using a viscous fluid to allow slippage 
of the hub in the outer body.  A "non-thermal clutch", when fresh, 
should slip by approximately 70%.  As the clutch ages the slippage may 
increase to far more than that, and lead to a lack of sufficient air 
being pulled through the radiator and overheating - especially at idle 
speeds.

The "thermally activated clutch" has a bi-metal coil on the front of it 
to sense the air temperature as it comes from the radiator.  When the 
heat rises it sets off a valving change within the clutch. Normal 
rotational speed of a thermal clutch should be, as in the non-thermal 
one, something like a 70% reduction.  But when the radiator rises to a 
certain level, the fan will speed up to somewhere around a 30% reduction 
instead.  You can hear the fan speed up and slow down as you drive under 
demanding conditions - and that's, frankly, a reassuring sound to hear 
it doing its job.

I can't say how the engineering decisions were made regarding all the 
variables of clutches, blades and shrouds on the various years, models, 
and engines, but we can be sure the bean counters had a role in choosing 
the least costly way to keep a given engine just cool enough.

Keith Boonstra

-
On 7/25/2012 12:17 AM, 2HsandaHeritage@xxxxxxxxxxx wrote:
>
>
>
> Hi Group,
>
>
>
> I am somewhat confused about the operation of fan clutches and the 
> reasons for their use.
>
> My questions apply to 1962 vehicles with 413 engines because I am 
> familiar with them and have the parts book.
>
> A 300H w/o air has a fan clutch and 7 blade fan.
>
> A 300H w/air has a fan clutch, 7 blade fan and a shroud.
>
> A New Yorker w/o air only has a 4 blade fan.
>
> A New Yorker w/air has a fan clutch, 7 blade fan and a shroud.
>
>
>
> I have always thought that the purpose of a fan clutch was to lessen 
> the energy required to rotate it when it was not needed for cooling.
>
> I also thought that the viscosity of the fluid in the fan clutch 
> changed with temperature so that it would increase in rpm to match 
> that of the water pump when needed for increased cooling.
>
> The shroud on air conditioned cars is there to help the 7 blade fan 
> pull more air through the radiator that is blocked by the ac condenser 
> in front of the radiator.
>
>
>
> The above makes sense to me except for the difference between the 300H 
> w/o air and the New Yorker w/o air.
>
> Why would the New Yorker only have a 4 blade fan and no fan clutch? 
> Perhaps robbing HP was not considered important for tha New Yorker.
>
>
>
> Doug Warrener
>
> Fair Oaks, CA
>
> 300H
>
> 62 300 Sport Conv.
>
>
> [Non-text portions of this message have been removed]
>
> 



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