Message text written by INTERNET:McGaheyRx@aol.com
>Not sure what you mean by "not as good a coolant" - surely you don't mean
antifreeze/water doesn't have a higher boiling point than pure water - it
most
definitely does. The principle by which this works (freezing point
depression/
boiling point elevation) also explains why you don't ever want more then
50%
antifreeze - beyond that point the freezing point comes back up and the
boiling point comes back down. You need the right mixture to get the best
protection from freezing and boiling.
<
What Randall meant is that water has a higher Specific Heat than does
Ethylene Glycol. This is a measure of how much heat it takes to raise the
temperature of a substance a specified amount. For example it takes one
BTU to raise one Lb of water one degree Fahrenheit. The specific heat for
EG is less. This means that in order to conduct a given amount of heat
from the engine to the radiator the H2O/EG mixture will have to have a
higher temperature differential.
Additionally, Ethylene Glycol has a lower density so a given volume of
mixture will have less matter so the pump is actually moving a smaller
number of molecules which means, what? A higher temp differential!
So, in a situation where the temperature is not controlled by the
thermostat, the coolant exit temperature (as measured by the gauge) will be
lower if you are running straight water as opposed to a mixture.
As far as freeze protection goes, they used to use alcohol before they
development of ethylene glycol but alcohol is volatile and will evaporate
over a short time and it offers no boiling point extension. EG will
provide both boiling point extension and freezing extension and it doesn't
go away. And the boiling point extension somewhat compensates for the
higher temperatures experienced as a result of the lower specific heat.
Optimum freezing protection is offered somewhere around 70% EG/30%H2O.
Concentrations of EG greater than that will freeze at a higher temp. When
I asked my dad (the chemist) why that was so he said that water lowers the
freezing point of EG in the same way that EG lowers the freezing point of
water. Just like a lead/tin mixture will melt at a lower temperature than
either metal alone.
Living in the midwest I use a 50/50 mix. It provides protection to at
least -30F (-35C), cools just fine in the summer (and it gets plenty hot
here) and it is easy to proportion out - I pour half a bottle of antifreeze
into an empty container and then top up both with water. I then have two
gallons of premix.
Dave
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