In a message dated 1/13/2001 8:38:28 PM Eastern Standard Time,
william.eastman@medtronic.com writes:
<<
I must throw another tuppence on the thermostat issue, however.
Slowing down flow in the radiator reduces efficiency and will not aid
cooling. The thermostat, especially when fully open at idle, will not
significantly slow down the flow in any case.
Also contrary to what is often said, an open thermostat won't increase
pressure inside the engine- at least not at idle. There simply isn't
enough flow to do this. At high RPM I could see where this could be a
factor in some cases. Even then, I would suspect that it's effect on
pump cavitation would be as great or greater than any effect on boiling
temperature. If your t-stat isn't fully open when you overheat, then I
think you have already identified the problem;-)
What I suspect a thermostat does is impact the coolant flow or level
inside the engine. The pressure drop between the front and back of the
head is very low and subtle changes can effect flow patterns. This, in
turn, could improve rear cylinder cooling or (a remote possibility)
scavenging of air pockets. For instance, the thermostat could change
the flow velocity profile and cause fluid flow in a critical area to
change from laminar to turbulent. Turbulent flow cools much better than
laminar and the world is once again safe for old English cars be they 3
or 4 wheeled.
You hear about how adding a thermostat helps cooling so much that, in
my opinion, the effect can't be dismissed. You can't violate the laws
of physics, however.
Fred, as a last point, wasn't the Ford engine in your 3-wheeler
originally syphon-cooled? I admit to complete ignorance when it comes
to these and would love to hear of your experience.
>>
Yep... but folklore/racing wisdom was to add a waterpump. Instead.. I use a
100E engine which has a pump. I run an IOE head (intake over exhaust) which
had no provision for a thermostat- it never did come up to 180- even when
raced- so I installed an inline thermostat by making a housing for the top
hose-now it goes to 190 and stays there. I believe in thermostats for engine
life. I DO have a good radiator...
Slowing down coolant flow through the radiator may decrease efficiency in
theory, just as you stated- the greater temp differential will increase
efficiency too... but... "effency" is not all we want- gotta work within the
parameters- the coolant has to have a "residence time" in the radiator (which
doesn't "radiate" much..) and this is a factor in designing cooling systems.
Of course engineers do it all very scientifically. everything can be
calculated and measured... They know how many BTU's gota be dispersed, latent
heat factors of the coolants, coolant flow rates, heat dispersion rates of
the radiators at given airflow-temp-flow, etc... We (I) on the other hand are
"puttin' a bunch of stuff together" and hope it works-
Cavatation is a problem at high rpm's.. Again pumps are probably most
efficient at moderate- everyday driving, rpm's. That is where they are
designed to work.. by some engineer. Racers do all kinds of homebrew stuff to
try and prevent this such as cutting off every other blade or reducing the
depth of the blades. A lot of it works!
I made a smaller crank pulley to reduce impeller speed to reduce cavatation.
I really like Smoky's reverse flow cooling- Evans does the same thing- put
the cool stuff to the head and run it down through the block. 'Course with a
sixty-year-old car....
I like all the theory stuff except that it makes my hands colder- feels that
way every time I get in my car in the winter and remember that the wheel
making my hands cold because it is sucking the heat out of 'em. I hate the
thought of having my heat sucked out, it was not so bad when I just thought
the wheel was cold...
fred
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