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RE: Exhaust &
There are two factors that I think you should consider in deciding what mixture you should use in a liquid cooled system. Protecting to 18deg F on the ground could get you into trouble while flying. At, say 15,000 ft., the OAT is -30degF. and a normally aspirated engine is capable of less than 50% power, the flow through the radiator is very small. The low flow will unload the water pump and the power used is insignificant. The low flow will also allow the coolant to freeze in the radiator.
Sent: Monday, June 29, 1998 5:18 AM
To: Velocity List-Reflector
Subject: Re: Exhaust &
> From: "R. Wayne Owens" <firstname.lastname@example.org>
> on me: since water boils so much better at our cruising altitudes, do
> you use PURE coolant and/or what psi radiator cap are you gambling on ?
> I examined my radiator cap and it appears that spring pressure alone ,
> not spring and atmospheric pressure regulates the system pressure.So
Actually, any radiator cap will only be X PSI above ambient air
pressure, no matter what that is. So at 18,000 feet, a 22 PSI cap
would act about like a 15 PSI cap at sea level. Concidering that the
standard temperature up there is -5.3degF, I wouldn't sweat it much.
Pure water (Plus corrosion inhibitors.) has some nice properties if
you can get away with it. The normal fifty-fifty coolant mixture is
almost four times thicker than pure water, increasing the HP needed
to pump the stuff, which means more fuel used, more heat added to the
coolant, more radiator area needed, etc. A 50/50 mix also has a lower
heat capacity, so for every pound you pump through the radiator, it
can carry less than 80% the heat of pure water.
I don't have numbers for how much antifreeze increases the boiling
point, but just as important (or more so) is the lowered freezing
point. Here in Georgia, I could easily get away with pure water for
most of the year, and go with a 20/80 mixture for the winter. A 20/80
mix won't freeze till about 18degF, which is fairly rare in my area,
and it's less than 70% thicker than just water.
Redline(?) has a product called 'Water Wetter' that's a corrosion
inhibitor and has a wetting agent that's supposed to increase the
heat transfer from the coolant galleries to the coolant.