Date:         Mon, 12 Jun 2000 23:07:36 -0400
Reply-To:     Marc Perdue <marcperdue@ADELPHIA.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Marc Perdue <marcperdue@ADELPHIA.NET>
Subject:      Re: Detection of air bubbles in coolant system
Content-Type: text/plain; charset=us-ascii

This doesn't make sense to me.  The cooling system in the Vanagons is a
pressurized system.  Unless the coolant is a compressible fluid such as
freon, it seems to me that you'd HAVE to have SOME air in the system.

What am I missing?

Marc Perdue

kenneth d lewis wrote:

> 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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