Uh, Jim, I'm not sure you can really apply the Ideal Gas Law to a
liquid...
But the system is pressuized, to either 7psi or 15 psi, depensing on the
rating of the radiator cap. This pressure effectively raises the boiling
point of the liquid, a good thing, since you don't want your coolant
turning to steam, since steam doesn't cool as well :)
With the system open, you're just measuring the temp of the liquid, and
as long as it's less than 212F (at sea level), evaporation for this test
should be negligible. So since we have a liquid in the first case
(closed, pressurized system), and the second case (open system), I think
that the thermometer method is a valid way to see if the temp gauge is
reasonably accurate.
If, for some reason, there's vapor in your cooling system, then the
ideal gas law will come into play (partial pressures and all that), but
by that time I'm sure you've got bigger things to worry about! :)
Cheers!
-=Chris
Chris King
http://home.comcast.net/~kvcbk/
<-----Original Message----->
From: Jim Johnson [bmwwxman@gmail.com]
Sent: 5/25/2007 2:17:56 PM
To: abcoz@hky.com
Cc: bugi1960@gmail.com;spridgets@autox.team.net
Subject: Re: Overheating woes > Water Wetter
Bud wrote:
Years ago, I stuck a
> thermometer in the radiator tank, with the engine starting from cold,
> idle, and just noted what the thermometer read, compared to the gauge,
> as the engine warmed up. Pretty easy to do, and it won't puke much
> coolant out of the open filler plug hole, while idling.
Bud.... This also won't give you an accurate temperature! Recall:
PV = nRT
Temperature (T) is inversely proportional to P (pressure) and V
(volume). If you leave the radiator cap off, the system is not
pressurized thus Temperature will be different than if the system is
pressurized as it normally would be.
Big question which I alluded to the other day when Frank had his
problem - "Is a spridget cooling system pressurized??" If it isn't,
you are okay, but I'm thinking it has to have at least some pressure
in it due to expansion from heat and the fact that the system is
closed.
Cheers!!
Jim - 68 Midget in Dodge City
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