The physics and engineering are clear and indisputable with respect to
heat transfer rate versus coolant mass flow rate, whether we are talking
about engine coolant (water/ethylene glycol) or radiator coolant
(airflow). Increasing flow rate will, without exception and all other
factors being equal, increase the heat transfer rate. Conversely,
slowing the mass flow rate will reduce the heat transfer rate resulting,
in the case of automobiles, in poorer performance. To argue this point
is akin to arguing that the earth is flat. I have spent better than 20
years in the engineering business which has included design and
development experience in thermal control systems for spacecraft, launch
site HVAC systems, and as a graduate student solar heating systems,
involving the use of heat exchangers and radiators quite similar to
automotive systems. I hope you will trust me on this one! That being
said, we should recognize that we have been discussing a fairly complex
system in very simplified terms. Thus we can't possibly expect to
achieve a complete understanding of the cooling system behavior for all
automobiles as a result.
I believe at this point the focus of the discussion should be on trying
to determine, as some have claimed, if there are indeed instances when
removing the thermostat results in increasing engine temperature, and if
so why. Clearly this is an anomaly (with respect to our simplified
discussion) and if it actually occurs it is the result of some other
factor which I would like to know about. I spent several years, prior to
becoming a mechanical engineer, working as an automotive tech and never
witnessed a case where removing a thermostat would increase engine
operating temperature. Nevertheless I have learned over the years to pay
attention to real world experience rather than dismissing it.
There are only two ways to resolve Gregs conundrum. The first would be to
investigate a specific case, where it is believed that removing the
thermostat increases operating temperature, to determine if that is
actually what occurs and if so determine the mechanism responsible. This
would entail operating the engine at identical operating and
environmental conditions with and without the thermostat installed and
with the engine fully instrumented, including judiciously placed
thermocouples, mass flow sensors, etc. to accurately determine the
actual engine operating temperature and heat transfer rates. Once the
behavior is either confirmed or disproved one could begin to determine
with a series of tests and/or analysis what mechanism is responsible for
the behavior. Some postulates could be (admittedly WAG's) the
possibility that the absence of the thermostat is resulting in cavitation
at some point in the system (pretty unlikely) or maybe that the radiator
bypass is having an unexpected affect or simply that the engine temp
gauge gets a bad reading? Most likely it would be something
unanticipated.
The second approach would be to inquire of an expert in cooling system
design if such behavior has been observed and explained. I have no doubt
that the auto manufacturers have run an endless number of tests on
cooling systems and could readily resolve this particular issue (assuming
you are willing to accept their expertise!). Anybody know somebody like
that?
Meanwhile if anyone cares to tackle conducting a controlled experiment as
I have described I would be very interested in the results. In fact, if
I had a vehicle with that kind of behavior I'd do myself! Also, if
anyone has had experience with this type of behavior I would personally
appreciate hearing about it with as much detail as you can provide
regarding the vehicle and engine type and conditions under which you saw
an operating temperature increase after removing a thermostat. I'll keep
checking into it and if I come up with any answers I'll let you all know.
Otherwise, I concur with Greg - there's probably not much more to be
gained by continuing the discussion but I hope that we have all learned
something useful from the exchange.
Andrew
----------
From: Greg Monfort[SMTP:wingracer@email.msn.com]
Sent: Wednesday, September 08, 1999 10:18 AM
To: Bricklin
Subject: Fw: COOLING SYSTEM
Air flow increases, but until the fan clutch is engaged, it's increase in
cooling effect appears to be marginal with rising RPM. Once engaged, it
still doesn't seem to help much, if any at rest. To use your test, rev
the
motor while stopped in traffic and see if the motor cools down.
You keep avoiding the questions posed, and earlier in the post that you
snipped I gave my thoughts on the probable results of such a restrictor
test. Anyway, most of us have a variable restrictor already, it's called
a
thermostat.
I neither believe nor disbelieve what's taught in Physics books, but how
they apply in a car's coolant system, since the results don't seem to
always
'follow the rules'.
Unless you can enlighten us on the conundrum, we're down to wasting BW,
so
until then we're done.
GM
----- Original Message -----
> >According to you, we have a second option of revving the motor to
> >increase flow. AFAIK, that ain't the way it works, it just gets
hotter.
> >
>
> Wrong. Increasing RPM (to 2000 or so) increases both airflow and
coolant
> flow and the engine cools down.
>
> If you do not believe thermodynamic theory as taught in physics classes
> around the world and want to disprove it, you are free to do so, but
please
> stop trying to get someone else to risk their car to run your test. I
> believe the standard theory ( more fluid flow : air and/or
> water = more cooling ) and followed it successfully in my car. Put a
> restrictor in YOUR radiator and test your theory. Cut a metal disk to
fit
> in the radiator neck
> under the thermostat. Punch a small hole in it (a nail will work fine)
-
> the smaller the hole, the more cooling per your theory. This is
neither
> expensive nor difficult. Take your car out in 5 O'clock rush hour,
stop
and
> go traffic on the Interstate in 95 degree temperatures. The most
likely
> event is that you will have to pull over and remove the restrictor.
The
> worst that should happen is that you will
> damage your engine. Let us know if we should throw away our physics
> textbooks - after you have conducted the above experiment.
>
> Mike
>
>
>
>
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