> >>> >I disagree with the writer that suggests a 50/50 mix of antifreeze. That
>is
> >>> >fine for winter driving, but in 85+F. weather, you may boil over as the
> >>> >antifreeze lowers the boiling point as well as lowering the freezing
>point
> >>> >(which is irrelevant here). I'd like to see more discussion on the topic
>of
> >>> >coolants.
> >>> >
> >>
> >>The antifreeze shouldn't alter the boiling point significantly. What does
> >>alter it is the pressure of the system. An open (unpressurised) system
> >>boils at around 212 F. The same system at 15 psi boils at 265 F.
> >>Pressurre is the key to preventing boil. I don't have the formula so
> >>can somone tell me what temperature my '67 B will boil sith the 7 psi
> >>cap?
The following information came to me via direct e-mail from an
enthusiast in Florida, in response to one of my posts (in which I quoted
my ant-freeze bottle as showing a 14 degree increase in boiling point of
a 50/50 mixture vs. pure water). Said enthusiast was hesitant to
respond to the MG list due to a reluctance to step on anyone's toes
(must be some big, sensitive toes out there!). Not being one to avoid
trodding all over other's feet, the following is probably more than you
ever wanted to know about the composition of anti-freeze!
"From my schooling days (many years ago) for every one pound increase
in pressure, the cooling system boiling point increases 3 degrees (F).
This is a general "Rule of Thumb" which almost everyone in the industry
uses. To get exact you have to do the math and calculate in the factors
for
the barometric atmospheric pressures & elevations. Three pounds works
out close enough.
Anti-Freeze (100%) has a heat transfer rating that is 25% of plain
water. [Littlefield's note: Wow! I wouldn't have guessed that heat
transfer would be that much less! As I noted in an earlier post, some
transferability can be regained by using Redline's Water Wetter]
Water EtGly PropGly Units
boiling point 100 197 188 deg C
freezing point 0 -13
deg C
molar heat capacity 18 36 45 cal/mol-C
specific heat 1 0.58 0.59
cal/gram-C
vapor pressure at 25 C 24 0.12 0.13 torr
molecular weight 18 62 76 gram/mol
heat of vaporization 9.72 12.06 12.94 kilocal/mol
heat of vaporization 540 195 170 cal/gram
viscosity at temp. 1 @ 20 C 13.6 @ 30 C 18.0 @ 40 C
The ideal temperature for coolant is 190 F.
BTW - I live in Florida and rarely see freezing temperatures, everyone
here
still relies on anti freeze and refers to it as ''coolant''.
See Ya, <name withheld>"
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