Here's some thoughts from the "engineering department" on the engine cooling
thread.
1.. Ask: What are the real reasons for cooling an engine? I'd say to "to
minimize temperature differential effects in close clearances, keep oil
viscosity in the range for best bearing surface performance and keep
temperatures low enough to prevent fires." (think about air cooled engines)
2.. Higher coolant fluid velocities remove more heat. Primary reason is
that more cool water touches the hot surface in a given amount of time. This
is pretty intuitive. Secondary reason is that higher fluid velocity means
more turbulence, which carries hot water away from the surface layer.
3.. The radiator transfers heat from water to air. How much depends on
water and air, flow and temperature. But the heavy hitter here is the
difference between water and air temperature.
4.. So you raise the water temperature. Higher temperature differential
means more heat can be removed by the radiator. You prevent excess steam
formation from blocking cooling passages by raising the water pressure which
raises the boiling point. You also raise boiling temperature some by adding
ethylene glycol (EG). But glycols carry less heat per pound than water. So
for most purposes the "break even" point is a 50-50 mix.
5.. Propylene glycol is interesting stuff. About 2 or 2-1/2 times the cost
of EG. But it's non- toxic. There's even an FDA approved food additive grade
of it. You can run much higher jacket temperatures with it. That means
thermal expansion problems are magnified. (note all that accurate machining
and engine assembly was done at room temperature). Can't comment
intelligently about performance gains possible from running high cooling
jacket temps. Might be some materials problems for cooling system components
like hoses, pump seals and gaskets. Coolant lines may represent a little more
of a burn injury hazard.
Enough on the subject today. Brace yourself for more tomorrow.....Ed Weldon
|