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## Re: Overheating woes > Water Wetter

 To: "Chris King" Re: Overheating woes > Water Wetter "Jim Johnson" Fri, 25 May 2007 16:25:40 -0500
 ```Chris, Now you have me curious... Time to drag out the old fluid dynamics texts and the CDC book. ;-) I am thinking that gases *are* fluids of very low density. I'm a meteorologist and we apply the same laws to the atmosphere that hold for fluids. Some adjustment to the equation for density of the fluid ("rho" which would be Mass / unit Volume) gives one P =(rho)RT. Now you can make the fluid dense and turn it to liquid if you wish and P is still inversely related to T, right? I'll look this up tonight. It's been a very long time since I messed with this and you've made me curious... Cheers!! Jim On 5/25/07, Chris King wrote: > > 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 > > > . > -- 1964 R60/2 BMW 1968 MG Midget 1976 R90/6 BMW 1990 K100LT BMW Thomas Huxley - "It is not who is right, but what is right, that is of importance." ```
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