WARNING!!!!! "M" rated!!!!!!
Don't read this if math makes your head hurt.
Dave Binkley wrote:
> "25 Lies Car Magazines Have Told For Years".
>
> "Lie Number 9: ... Glycol has a higher boiling point than water, but
> even when using a 50/50 water/glycol mixture with a 15-psi radiator cap,
> glycol's boiling point is only 15 degrees more than plain water....
>
> Dave
My Prestone container says a 50/50 Prestone/Water mix freeze protection is 34
degrees below 0 F and the boilover is 265 F, with 15 psi pressure. Normal pure
water boils at 212 F at sea level.
A little calculation, based upon the Handbook of Chemistry and Physics (The
Rubber Bible) reveals:
delta T = ((273.1 + T) x (2.8808-log P))/ ((Entropy of Vaporization) + (0.15 x
(2.8808 - log P)))
Since I can't send greek symbols, the words will probably be better anyway.
delta T is the difference in boiling point
T = the original boiling point (100 deg C at sea level 14.7 psia)
logs are all base 10
P is the new pressure, in mm of Hg. 15 psi is about 760 mm Hg, which is about
the same as the sea level pressure
The Entropy of Vaporization (greek phi) is 5.7 for water at 100 C (original
boiling point)
The answer is 20 degrees C change. Using (9/5 x C) + 32, this is 36 deg F
increase.
New Boiling Point is 212 F + 36 F is 248 F, using water alone, and an additonal
15 psi.
265 F (Prestone) with cap - 248 F water with cap (calculation) = 17 F better.
Of course you can check the math out, if you wish.
So, your quotation is verifiable by physics!!!!!!! What's 17 degrees more
protection worth?
If it's the difference between boil-over, or not, with your engine, a lot,
IMHO.
Now this all assumes you have truly distilled water, and no dissolved minerals
from your engine to change this calculation.
{:-{>
Professor Steve
--
Steve Laifman < One first kiss, >
B9472289 < one first love, and >
< one first win, is all >
< you get in this life. >
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