Message text written by Barry Schwartz
>>>Engine cooling fans are typically fed by "always on" current, not from a
>>source that would require the ignition to be in the "on" position. The
>>reason for this is so the fans can run a while after the engine is
>>switched off (to speed cooling of the radiator once air flow from
>>vehicle movement is no longer present).
>****************************************************
>While I *used* to have my fan switch this way, I no longer have it wired
up
>like that now for other reasons. While I can see the logic, in that it
>WILL cool the radiator (and not much else when the engine stops running) I
>don't really see the *NECESSITY* for it. Granted there is a slight
>advantage in that it will help keep the water from boiling in the radiator
>but that's about it. <snip>
Barry, while I agree with your statement about the fan cooling the radiator
and not much else but I mus tinterject that the coolant in the radiator
dies not boil after engine shut-down with or without fan. The water boils
in the engine (due to hot spots) and comes out of the radiator. And, as
you stated earlier, the fan does little to cool the engine.
The main advantage fo the "always on" configuration is simplicity. All you
need is a hot wire, a thermoswitch and a fan. If you tied it into the key
you would need an additional keyswitch contact with a 20 amp capacity or a
relay and in an industry where every penny counts you eschew every
unnecessary expense possible. I find it annoying when a fan continues to
run (or often enough start to run) as I walk away from a car I have just
shut off. My AUDI 5000 would do that but I think it was to cool the
turbocharger - the fact that my car had no turbo notwithstanding.
Your comment about cars with belt driven fans not suffering from the lack
of forced air cooling after shut off was right on.
Cheers
Dave
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