Lynn Hanover wrote:

You [Thomas Parkes --rak] might try making that a 90/10 glycol mix. Much better
heat transffer. And run a 22 pound cap.

Whoa! Let's look at what running a 90% water, 10% ethylene glycol mix might do
first.

  1. According to ASTM D11777, the freeze point of a 10% solution is 26 deg F.  I
     dunno where Thomas Parkes parks [ok,ok, no more puns] his aircraft, but this
     might be a big problem for him in the winter.
  2. Furthermore, that same test indicates that the "slush point" (where ice
     crystals form in the solution) can be as 30 degrees warmer.  While obviously
     no ice crystals are going to be forming at 56 deg F, it is likely that the
     coolant will begin to freeze at 32 deg F.  What most people don't know about
     the "freeze point" of antifreeze is that it is set in reference to a hard
     freeze of the material (effectively the "copper pipe burst" temperature).
     Prior to this hard freeze, however, the solution gradually turns into a hard
     slush that can easily damage more delicate parts.
  3. Antifreeze manufacturers formulate their products to be used in the 40% to 60%
     solution range.  This is because of the additive package.  It has all sorts of
     useful things in it like cavitation protectant (nitrite), aluminum corrosion
     inhibitors (silicates), ferrous metals corrosion inhibitors (nitrate), etc.
     If one greatly dilutes the antifreeze, there may not be enough of the additive
     in the coolant to do the job.  For example, ASTM D2809 specifies the
     cavitation and erosion corrosion test for engine water pumps.  Most (all?)
     automotive antifreeze products meet this standard when used in the 40% to 60%
     dilution.  Over dilute, however, and the package may not protect sufficiently,
     which could lead to premature failure of the water pump.

Were I Thomas, I'd use a 40% automotive antifreeze solution using *distilled* 60%
water, keep the 13 p.s.i. pressure cap, calibrate the temperature sender using a
pot of boiling distilled water, locate the temperature sender as close to the block
outlet as practical, leave the alarm setpoint at 220 deg F, and sleep well.

Russell Kent

Well sounds good but if he takes off and it boils over on climb out he is
in deep doo doo. I think he needs more of a margin than that. What is your reasoning
on only a 13 psi pressure cap?

Paul Lamar
 
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