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

Perry Mick wrote:

A 16 lb. cap worked fine for me last winter, but when summer came I had
to go back to my 24 psi cap.

Perry

 
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