Date: Mon, 12 Jun 2000 21:13:00 EDT
Reply-To: kenneth d lewis <kdlewis@JUNO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: kenneth d lewis <kdlewis@JUNO.COM>
Subject: Re: Detection of air bubbles in coolant system
John;
The best sign is NO air in the coolant system, and there you go
pumping air into it! If it ain't broke don't fix it! As long as ther is
NO air in the reservoir everything is fine. That's the best check you can
make.
Drive Safely & Good Luck
Ken Lewis <Kernersville,NC>
86 VW crewcab;60 356B Coupe
--------------------------------------------------
On Mon, 12 Jun 2000 13:32:52 -0400 "John W. Parkins" <jwp6@PSU.EDU>
writes:
>I had some thoughts on coolent system air bubbles, and thought I would
>share them.
>
>First off, I changed the heads on my 87 Westy, and wanted to be able
>to
>check for leaks in a convenient way. I put together a pressurizing
>system
>that was suggested by a listserver member. My design was slightly
>different. I found a brass T fitting at my local hardware store.
>They
>also sell a bicycle pump adapter that will screw onto the T. The
>store
>also sold a pressure gauge that would screw right onto the T. You then
>clamp a thick hose onto the T that will also fit on the coolent tank
>(not
>the expansion tank). Take off the expansion tank hose and clamp on
>your
>pressurization system hose. Use a bicycle pump to pump up the coolent
>system to 14psi. You can then remove the pump. If the cooling system
>doesn't hold pressure, look for the leaks. This rig costs around
>$10-$15,
>and is well worth it. (You can't use this system to measure the
>pressure
>generated in the cooling system when the engine is running though.)
>
>Now, I found that I had no leaks in the system, but the temperature
>was
>reading high by about a needle's width. When I pumped up the coolent
>system, I found that the level went down at least three inches. Now
>here
>is my thought. Since the fluid is basically incompressible, the fluid
>must
>have gone into air pockets. Now the pressure times the volume of the
>air
>in the coolent system is a constant (if you allow the system to remain
>at
>constant temperature), or P1*V1=K (V1 is the initial volume of the air
>pockets, and P1 is the pressure in the air pockets). Now if you pump
>up
>the system, you get a new pressure and volume and P2*V2=K. If you pump
>up
>the system to 14.7psi, you have doubled the pressure in the system
>(since
>atmospheric pressure is 14.7psi). Thus P2=2*P1. Now, the change in
>volume
>of the air bubbles is V1-V3, where V3 is the volume of air pumped into
>the
>coolent tank (which can be estimated). Now, P1*V1=P2*V2 and V2=V1-V3.
>So,
>V1=2*(V1-V3). Solving for V1, V1=2*V3.
>
>In other words, if you pressurize your cooling system by pumping air
>into
>the coolent tank ( to achieve 14.7psi), and the cooling tank level
>goes
>down, there is air in your system. The amount of air in your system
>is
>equal to twice the volume of air you pumped into the cooling tank.
>
>Any comments on this? I think it is a good way to determine how much
>air is
>in your cooling system. I have a significant amount of air in my
>system,
>and I think this is the reason for the higher temperature reading.
>Cheers.
>
>John
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