The fan clutch is a bit of both. It reacts both to rpm and to temperature,
hoping to achieve the good effect of
pulling air through the radiator only when it needs to.
Failure of the units is usually detected by seeing the fan slowly turning
with a hot engine.
They aren't my first choice for a cooling fan, but they've worked pretty
well in those applications where I had them as oem installations.
----- Original Message -----
From: "Larry Vaughan" <ljvaughan@pldi.net>
To: "Joe Curry" <spitlist@cox.net>
Cc: <spitfires@autox.team.net>
Sent: Tuesday, August 21, 2007 7:07 PM
Subject: Re: [Spits] fan clutch
> Hey Joe,
> That explains why a ford or chevy heats up driving thru mud, the ones
> with viscous couplers known as clutch fans anyway. So the improvement
> over fixed fans may not have been much of an improvement. Electric fans
> appear to be the best bet, if you don't blow a fuse.
> I should probably use the 1973 fixed fan. Its light weight plastic.
> Let me hear some opinions on the best fan setup. I am aware that an
> electric fan mounted on the front of the radiator blocks airflow at high
> speed, so it is not much of a back up except in town.
>
> Larry
>
> Joe Curry wrote:
>> Larry,
>> I think you are talking about the "Viscous coupler", which is not a
>> clutch
>> at all and as I understand the thing it does not react to temperature at
>> all. Instead it is designed to limit the fan speed at higher rpm to
>> reduce
>> noise and limit the pull don on the engine as it virtually free wheels at
>> higher rpm. I think the theory is that it pulls when you are driving
>> around
>> town where the speed is not sufficient to keep natural air flow through
>> the
>> radiator. When you are at speed the thing free wheels allowing the
>> natural
>> air flow to cool the engine.
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