I have switched back and fourth between antifreeze/water mix and
NPG and there was no temp change between them.
   Ken Welter

Wow, if I find that to be true in my plane then I will be very happy and
impressed.  Keeping the temps equally cool while elimiting the risk of boil
over sounds very appealing.

Dave Leonard

It can fool you. The coolant temps can be the same but the metal temps
can be higher. The only way to really know is with an embedded thermal
couple near the lower spark plug within one mm of the combustion chamber.
The second chart showing the ratio of housing temp to coolant temp is
only good for ethylene glycol mix and not necessarily for propylene glycol.

Basically the rate of heat transfer from metal to coolant is a function
of the coolant viscosity. 5 weight oil cools better than 20 weight oil
for one example.

I am not saying the engine is going to melt. I don't know the implications
or by how much the metal temp will be higher. It may have some implications on
spark plug life or heat range.

However the lower heat transfer to the coolant is definitely a plus
in theory as far as BSFC is concerned.
 
Paul Lamar
 
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