"Niamh Holding" <
[email protected]> wrote in message
news:
[email protected]...
> In article <[email protected]>,
> [email protected] (Badger) wrote:
>
>> 100% more foolproof
>
> You'll love the one we've just pulled out of a Discovery that tended to
> run a touch hot under load. The hotter the coupling got the freer it got,
> so that you could stop it with your little finger, not that I was dumb
> enough to use my actual little finger 
>
Yes, I know that they can fail, but the people who advocate lecky fans in
the main are those who have had a viscous fail - a relatively small
percentage of total production, I'll bet!
Speaking as an engine builder now, I've yet to see a lecky fan setup that
can actually control engine temp as stable as a correctly operating viscous
can, and you ain't telling me that all the extra thermal cycling of the
engine block due to the lecky fans and the resultant expansion/contraction
doesn't contribute in some small way to premature head gasket failures. A
lecky fan tends to switch on too late to prevent the temp rising further as
the thermostat is opening and allowing an increased flow of hotter water -
it really needs to be winding up as the thermostat is opening but it can't
as it needs the thermal switch to make, and the hysterisis of these switches
is unacceptable, you either end up cooling too late, or overcooling. What is
required is a logic circuit of thermistors switching a resistor bank, but
that would push the cost beyond what your average joe public would pay.
Unfortunately in some motorsport disciplines where the engine is rear
mounted, the lecky fan is a necessary evil but even then I always install 2,
one running permanently and a second on a thermal switch as a safety measure
as I've seen too many fail!
Think also about energy paths-
Viscous; Mechanical > Mechanical, with a very low loss to heat.
Lecky; Mechanical > Electric > Mechanical, with much higher thermal
losses at each energy conversion.
The power to drive a lecky fan has to come from somewhere, and as you
increase the electrical load, so the alternator then consumes more engine
bhp. I seriously doubt any claims made by lecky fan manufacturers about
lower energy requirements.
Give me the reliability of a properly operating viscous coupling any day.
Badger.
