[FWDLK] Physics and antifreeze

[Bob Oswald <punch@xxxxxxxxxxx>]

Bill, you wrote:  "in physics pressure is directly proportional to
temperature (and
vice-versa) where volume remains constant".   This applies to a gas, but
not to a liquid.  Water essentially shows no significant change in volume
due to pressure or temperature changes until it reaches one of the
temperatures at which it "changes state" (solid to liquid and liquid to
gas).  This is obviously freezing point and boiling point of the liquid.
Antifreeze merely changes those points.
        You also wrote: "if you drop down to a 7-lb cap, you will also have to
change the
thermostat to a lower rating."  As was originally stated by Neil,
pressurizing a volume of water raises its boiling point by 3 degrees F for
every pound of pressure, thus no worry about boiling over with a 7lb cap
until 212 + (7x3) = 233 F.  And this is WITHOUT the effect of adding
whatever concentration of antifreeze you choose.  My '88 Suburban with a 15
lb cap runs at over 220 degrees on any long run towing a trailer, but that
is 37 degrees below its boiling point without benefit of antifreeze.  The
only potential problem with pressurizing older systems is their
susceptibility to water pump, hose and gasket bursts and leaks.  So there
should be no need for Neil to change the thermostat to a cooler one, since
even a 7lb pressurized system would give you 53 degrees of leeway above a
180 degree thermostat.
        Bob O. (Piled higher & Deeper)
PS.  Incidentally this phenomenon of soaking up heat until a change of
state results is why a/c systems can work so well:  in its liquid
(compressed) form a refrigerant like Freon or ammonia can soak up masses of
heat without expanding, but then when it is allowed to expand in the
evaporator (due to a sudden reduction in pressure), that heat is instantly
released and can then be exchanged across the condenser prior to being
recompressed into its liquid state by the compressor.



Date:    Sat, 13 Jul 2002 21:52:10 -0700
From:    Bill Watson <wwatson@xxxxxxxxx>
Subject: Re: New Antifreeze (was Mr. Dodge)

No line pressure?  No-pressure radiator cao?  No thermostat, too?    With no
pressure in the system, you must not have any temperature, either.  After
all, in physics pressure is directly proportional to temperature (and
vice-versa) where volume remains constant.   The other possibility is that
you do not fill the coolant system to capacity.  The expanding coolant will
take up the "unused" room.  (Air can be compressed more than fluid can.)

I don't think you have all the facts yet,

Also, if you drop down to a 7-lb cap, you will also have to change the
thermostat to a lower rating.  Again, it is that relationship between
temperature and pressure.   If you lower your rad cap pressure, and keep
your standard 180/190 thermostat, the rad cap will open as soon as the
thermostat opens.   Cars have 15-lb radiator caps to handle the higher
temperatures, which produces higher pressures.   If you go back to the days
when cars had 7-lb (or less) rad caps, the cars used a 150 or 160
thermostat.  (Which is one reason why heaters today are so much better - the
coolant they use is hotter now than before.)


Bill
Vancouver, BC

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