few more quotes from the grapeape site-last one is particularly pertinent.
"If the coolant begins to boil, steam pockets
will form and detonation will limit power (by forcing
you to retard timing to less than optimum or run the
engine cooler)...As coolant flows through the system it
absorbs heat from the engine parts that it comes in
contact with. As it does this some of the coolant will
boil and form tiny steam bubbles (absorbing a lot of
heat in the process) on the internal engine surfaces.
When these bubbles get larger they become a flow
restriction and the flowing fluid pushes them away
from the surface and that process starts over again.
The process is called the Nucleate Cooling
Phase. When the coolant boiling point is too low or
the flow rate is too slow, these bubbles can become
too large and form steam pockets that insulate that
surface from being cooled. This usually happens
around the combustion chambers, the hottest parts
of the engine. Once the steam pocket forms the
surface will rise in temperature (even though the
coolant is not overheating) and cause that part to
overheat, which can cause detonation and / or other
problems."
"I'm sure that you've read or heard
somewhere before that water is the best coolant.
This is true as far as being able to absorb heat for a
given flow rate, water does do that the best. Water
also boils at a lower temperature than other coolants
and can develop steam pockets easier, so it's not
the best coolant in that respect. A water / ethylene
glycol mixture will boil at a higher temp and resist
steam pockets better than plain water, the down fall
is that it has to have a higher flow rate, but that is
easy to accomplish."
"The pressure in the block is higher than the
radiator pressure; this is because the pump is
building pressure due to the thermostat being a
restriction. This pressure raises the boiling point of
the coolant and reduces the chance of steam
pockets, so never run with out a thermostat (or some
form of restriction).
The radiator cap will usually hold 15-18 psi,
if the radiator holds the system at 15 psi, the boiling
point of plain water will be raised to 250° F. The
water pump can then make an additional 40-45 psi
in the engine and bring that boiling point close to
300° F. So as you can see, pressure is important."
Topic: What are the Pro's and Con's of running a thermostat? (Read 5253 times)
