Hi Ken,
The theories vary. The one most acceptable to me is that the
thermostat/restrictor raises the local pressures in the water jackets,
especially around the exhaust valves, combustion chambers & reduces the
tendency for localized hot spots to vaporize the coolant (spot
flashing). With the restrictor, the localized (water jacket) pressures
can be much higher than the actual pressure cap setting.
The second benefit is that by raising the head pressure on the pump with
the restrictor, the pump inlet pressure is also raised (suction reduced)
which helps prevent cavitation of the pump. Cavitation is basically when
the pump creates so much suction that the fluid vaporizes in the pump
internals, which reduces pumping capability.
It's true that the rate of flow through the radiator cannot be too fast
for the coolant to be able to give up it's heat. With more flow, the
heat loss per pass through the radiator is reduced but offset by more
water passing through, so the two balance out. Flow tests have actually
shown that higher flow through the radiator can create turbulant
(scouring) flow in the radiator tubes which results in more "hot" water
being in contact with the tube surfaces. Slower, laminar flow, results
in the outer surface of the water column being cooled, but the inner
part of the column never contacts the tubes. So turbulent flow can
increase cooling.
Ref. "The Engine Cooling System" by "Technology Transfer Systems, Inc",
Livonia, Michigan.
Regards,
Dave Russell
BN2
Freese, Ken wrote:
> On this web site, I think there is a good explanation of why adding the
> thermostat aids cooling in some cases. Not because of slowing down flow to
> "absorb" heat, but by increasing the pressure. More pressure aids in the
> heat transfer.
> Ken Freese
> 65 BJ8
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