Re: [AMC-list] quiet in here, 195.6 ohv cooling system

[tom jennings <tomj@xxxxxxx>]

Cool, thanks! That solves it.

I'm sure the raised-pressure is PSIG, over atmospheric, so your 16 lb cap
would raise the boiling point of pure water 16 * 3 = 48 degrees F, or 212 +
48 = 260F. Duh, I forgot, I could have just looked at the steam tables and
water info in my CRC physics book! Why didn't I think of that?!

So not bothering to compensate for glycol under pressure, a 13 lb cap with
50/50 would be 223F plus 39F = 262F boiling point, minimum.

(You sure as crap don't want to pop the cap open when the engine is hot. The
towtruck driver on my ill-fated tow home last month did that on his
overheated big diesel truck (the duma**). When I saw him start on the cap I
got back 20 feet. The cap zoomed straight up 20 feet and was lost until I
found it 30 minutes later. I distinctly remember the ONE time I popped a cap
on a hot engine, my '62 Ambo, when I was 18. Peeled the skin off my
shoulder. Lucky it wasn't my face and eyes.)

There's probably a reason why most coolant temp gauges are calibrated for
280 full scale!



On Mon, Jul 19, 2010 at 1:46 PM, Frank Swygert <farna@xxxxxxx> wrote:

> I found a chart for plain water. Each psi over 15 psi (atmospheric
> pressure) raises the boiling point by 3° (212°F at atmospheric pressure).
> BUT, anything added to water will increase the boiling point/decrease the
> freezing point. So the ethylene glycol has that effect too.
>
> http://www.engineeringtoolbox.com/boiling-point-water-d_926.html
>
> Check this Wikipedia article out! It has the boiling point vs.
> concentration of ethylene glycol (anti-freeze). Assuming that the boiling
> point is raised the same as water a 50/50 mix would boil at 225° + 3° for
> each psi over 15 psi (14.7 psi).
>
> So a 13 psi cap won't work -- I run a 16 or 17 psi cap, which only adds
> 3-6°. Somehow that doesn't sound right. I know some engine run around 250°
> without boiling over. Is a radiator cap rated at psi over atmospheric? Then
> a radiator would run 225° + 36° (261°) with a 13 psi cap and 50/50 mix...
> which sounds about right...
>
> ---------------------
> Date: Sun, 18 Jul 2010 22:14:01 -0700
>
> From: tom jennings<tomj@xxxxxxx>
>
>
>>  " But 50/50 boils at 223F,
>>
>>  open air, or under the cap?
>>
>>
>>
> Oh right, 223F B.P. at atmospheric pressure. I can't seem to find a
> credible
> chart or formula for pressure vs. B.P.  but two random pages stated 48
> degrees increase in boiling point at 15psi.
>
> So coolant is NOT boiling in the head at 230F, so that is unlikely to be a
> problem.
>
> Still gotta find a chart or formula for this, but thanks Andrew!!
>
> --
> Frank Swygert
> Publisher, "American Motors Cars"
> Magazine (AMC)
> For all AMC enthusiasts
> http://www.amc-mag.com
> (free download available!)
>
>
> _______________________________________________
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>
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