I think that one very important factor has been ignored in this discussion
so far.
You want your cooling system to do _two_ things that are in some respects at
odds with one another:
1) Extract heat from the engine
2) Give off heat via the rad
It's clearly true that circulating a greater volume of coolant through the
engine in a given amount of time will increase the cooling capacity _IF_ the
temperature of the coolant as it enters the engine is kept constant. Note
that this breaks down for very high flow rates (where particle speeds reach
a few hundred miles per hour) where the kinetic energy of the coolant
particles slamming into the water jacket walls would give up energy to the
engine block. But realistically, at the temperatures and flow rates you're
going to see in an engine, this effect can almost certainly be completely
ignored.
However, it's also clearly true that leaving a given volume of water in the
rad for a longer time will allow it to cool more. So increasing the flow
rate through the rad decreases the amount of heat that can be dissipated
from a given volume of coolant for one cycle through the rad. Of course, if
the universe is gravitationally closed, then after a few dozen billion
years, the big crunch is going to drive the temperature in that rad way, way
up. But in that case, you'd have bigger problems. ;)
So, there are two opposing forces here: the faster the coolant flows through
the engine, the better able it will be to dissipate heat, and the slower it
flows through the rad, the cooler it will be when it re-enters the engine.
Depending on the slopes of these two curves, increasing flow through the
system as a whole could sometimes increase cooling effectiveness, and
sometimes decrease effectiveness. There are a lot of inter-related
variables.
You can't generalize and say that a greater flow rate through the system
increases or decreases operating temperature, because the cooling
effectiveness depends on both the flow rate through the engine (more flow
through engine = better cooling), AND the coolant temperature as it enters
the engine (more flow through rad = higher engine inlet temperature = worse
cooling).
Which is why the damn thermostat is in there. The thermostat regulates flow
through the engine to keep the temperature within a certain range so that
you don't have to figure all this stuff out for yourself. If the engine's
consistently running too hot, change the thermostat and flush the system to
get rid of air pockets and/or whatever gunk might be blocking the cooling
passages. If it's still running too hot, go with a cooler thermostat. If
it still can't keep up, you probably need a more effective rad, or the
engine's out of tune somehow.
Of course, as has been pointed out, if you only drive the car very rarely
the risk of the thermostat seizing might outweigh the inefficiency that
results from running without one altogether, so there are no easy answers.
Hope this is worth something,
--
Phil Martin pmartin@surgnav.com
"Who's my cream-puff?"
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