And I'm not trying to be argumentative, but if the
engine causes a "heat sink" to the radiator and the
radiator fan comes on cooling the radiator, isn't that
in effect creating a cyclical effect of reduction in
heat in the block? It just seems that, though it's not
very efficient since the pump isn't going, any
movement of air through engine bay will help dissipate
heat.
It may not be a lot of effective energy spent, but
when you're in 'errand mode' turning the car off and
on a lot, it does seem to help. Certainly seemed to be
more effective then my mechanical fan on the water
pump.
I was looking at the insructions for the thermostatic
switch I got from JC whitney ($45). It was also
equipped with a "switch wire" which only turns the fan
on while the ignition is on. But I simply wired it to
the same constantly hot source so that the fan is
completely controled by the thermostat. As I said
before, a simple mechanical thermostatic switch that I
use to have got cruddy and would stay on, or wouldn't
come on until you tapped on it. But the Solid state
unit has no moving parts to fail, so I'm less
concerned about having it wired constantly hot.
It seems that this switch was intended to only operate
while the ignition is on, but I know that most
contemporary cars do have thermostats or timers that
keep the fan running for a time after the engine is
turned off.
But I do agree with you. Do whatever works for you. If
it keeps your car happy and healthy, then it's all
good.
-Terry
--- Dean.Dashwood@enron.com wrote:
>
> Terry,
>
> Not particular important, but I thought I'd mention
> it anyway since you
> brought the subject up. I don't believe (and I'm
> sure other people will
> disagree with me) that leaving the fan running after
> the engine is shut off
> will help very much with the temperature rising
> after the engine stops.
>
> The reason the temperature rises is heat soak - the
> engine is hotter than
> the coolant, and since the two are in contact with
> each other, the heat is
> transferred from the engine into the coolant.
>
> Of course, this happens all the time when the engine
> is running, too.
> Except that when the engine is running, the water
> pump moves the coolant
> away from the engine into the radiator before it
> gets too hot. Once the
> engine has stopped, there is no movement of the
> coolant (except a very
> small amount due to convection) so it just sits in
> the block getting hotter
> and hotter.
>
> The reason I say that the fan won't help much is
> because the fan cools the
> coolant in the radiator - *not* the coolant in the
> block. And when the
> engine is not running, the water pump is not
> turning, so it's the coolant
> in the block which is heating up, not the coolant in
> the radiator.
>
> Of course, if you're happy with the way your car is
> wired, that's fine.
> But my fan is wired through my ignition switch (by a
> PO, not by me), and
> I'm quite happy with that.
>
> As always, any thoughts from people who know more
> about this than I do are
> welcome!
>
> Dean
> --------------
>
>
>
> Date: Tue, 3 Apr 2001 18:28:48 -0700 (PDT)
> From: Terry Thompson <firespiter@yahoo.com>
> Subject: Re: Switched power for fan
>
> <snip>
>
> And also the
> temperature seems to increase when you let the car
> sit
> for a few minutes (pressure cooker affect?). When
> you
> run into the store for five or ten minutes, it's
> actually hotter than when you got there. So I like
> having a fan that runs for a while after I get out
> to
> drop the radiator temp.
>
> - -Terry
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