writes: After you shut off your engine, the 7 psi gradually drops over the = next few minutes. It only takes around 12 minutes for the system to = develop a vacuum relative to atmosphere. At that point the little valve = in the radiator cap opens and allows fluid or air to flow into system. = (Check out your rad cap, can you find both valves?) --------------------------------------------- Al, if your cap is a 24 psi cap which you said you could run with = full bottle. Why does it develop a vacum on cool down. I have never = noticed this on my system, but on the other hand probably never looked = at it 12 minutes after shutdown ------=_NextPart_000_021F_01C56C74.0D240E00 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

In a liquid cooling system that has no=20 *non-condensible* gas (i.e. air), the pressure will rise due to thermal=20 expansion of the liquid, until it gets to the pressure relief value of = the cap,=20 at which pressure a small amount of the expanding liquid will go into = the=20 overflow bottle.

Upon cooling, the liquid volume = shrinks, and the=20 pressure decreases until it is lower than that in the bottle, and liquid = is=20 sucked back into the system. If the bottle is pressurized, then = the=20 pressure in the system will only go down to the pressure of the bottle. = This may=20 be what is being described in Dave's system.

Dave, do you have a *pressurized* = overflow=20 bottle?

Bill Schertz
KIS Cruiser # = 4045

----- Original Message -----
From:=20 WALTER B = KERR
To: Rotary motors in = aircraft

Sent: Wednesday, June 08, 2005 = 9:31=20 PM

Subject: [FlyRotary] Re: = coolant=20 leak

On Wed, 8 Jun 2005 19:05:25 -0700 al p wick <alwick@juno.com> writes:

After you shut off your engine, the 7 psi gradually drops = over the=20 next few minutes. It only takes around 12 minutes for the system to = develop=20 a vacuum relative to atmosphere. At that point the little valve in = the=20 radiator cap opens and allows fluid or air to flow into system. = (Check out=20 your rad cap, can you find both valves?)

---------------------------------------------

Al, if your cap is a 24 psi cap which you said you could run = with full=20 bottle. Why does it develop a vacum on cool down. I have never = noticed this=20 on my system, but on the other hand probably never looked at it 12 = minutes=20 after shutdown

------=_NextPart_000_021F_01C56C74.0D240E00--