Fred,
It sure sounds like Evans NPG is straight propylene glycol. Could the
NPG stand for "Neat Propylene Glycol"? Straight propylene glycol boils
at 189C which is 372F. They could throw in a few anticorrosion or
lubicant type additives which might reduce the boiling point to the 369F
that you mentioned.
A friend who races suggested that I try straight propylene glycol last
year when I was modifying my +4 to prevent overheating . We couldn't
figure out why it wouldn't be a good idea, but I decided to be
conservative and use a commericial propylene glycol/water mixture from
the local discount store instead. I like the propylene glycol better
than the more common ethylene glycol, because it is less corrosive on
the cooling system, doesn't effect paint in case boil over or leaking
water pump and is environmentally friendly. Also it won't kill the
neighbor's cat if it laps up a little puddle of it under your car. I
have actually been using it for years in all my cars even before it was
advertised for use in automobile cooling systems. I got tired of
replacing radiators and heater cores every 7 or 8 years in my everyday
cars and switched to "RV antifreeze" (propylene glycol/water mixture)
which prevented the corrosive action of the "normal" antifreeze.
I can't see why an engine would run any hotter with straight propylene
glycol than it would with a "normal" coolant provided you use an
appropriate thermostat. The advantage you would have is that when it
did get a little hotter than normal it wouldn't boil over, it would keep
on going and do a better job of cooling than a boiling liquid with it's
vapor pockets at the hot spots which need the most cooling.
Art Hart
Chester, NJ
'64 +4
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