Fred and Greg,
Thanks for adding information to my "book" dissertation. As a
mechanical engineer whose degree focus was IC engines, my viewpoint is
mostly shaped by the opinions of one Dr. Murphy (it pains me to realize
I no longer remember his first name and no, it is not THAT Murphy). Dr.
Murphy was a very good engineer and helped design aircraft engines in
WWII but he wasn't a car expert nor did he make any great effort to keep
up with the newest technology. His opinion was that the theory hadn't
changed so our late-forties text was sufficient. The only time we used
"modern" information was when we studied emissions.
Greg and Fred, on the other hand, have spent a lifetime keeping cars on
the road and working on race cars. Of the two, I take experience every
day over what "the book" says.
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.
Regards,
Bill Eastman
[This message delayed, as it needed manual intervention by the list
administrator. mjb.]
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