Date: Tue, 13 Jun 2000 22:29:38 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;
A proper working system bleeds all air out and draws coolant in.
I figure there's the expansion factor of the coolant to account for the
pressure increase.
Drive Safely & Good Luck
Ken Lewis <Kernersville,NC>
86 VW crewcab;60 356B Coupe
--------------------------------------------------
On Mon, 12 Jun 2000 23:07:36 -0400 Marc Perdue <marcperdue@ADELPHIA.NET>
writes:
>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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