Mailing List Message #625
From: Marc Wiese <>
Sender: Marvin Kaye <>
Subject: RE: [FlyRotary] Re: Coolant loss : More cooling system test stuff.
Date: Sun, 01 Dec 2002 15:55:11 -0500
To: <flyrotary>
> > .Tracy and others, what is the theory behind so much liquid in the
> external
> > expansion tank? Thermal expansion of the initial coolant volume
> > account for such a large overflow. So is vapor building up inside?
If it
> is
> > there is no longer a liquid filled system. I don't get it.
> > Peter
> I'm not 100% sure what is going on but I think you would be surprised
> much the 50-50 coolant expands with heat.  I flight tested the new
> yesterday and verified that on cooldown the system was completely
> off
> with coolant (no air at top of fill port.) This was never the case
> This also accounts for another anomaly I've noticed over the years.
> seemed like the water cooling was slightly better on the first flight
> after
> topping off the system.  I was never sure because the next flight was
> usually on a different day, different temperature, humidity, etc.  Now
> that
> I've been paying close attention I have verified that only a few
> worth of air in the system makes a noticible degredation in cooling
> performance  (about 5 degrees worth).   Not sure why this is happening
> either but I'm happy with the results.  With more experimentation the
> answer
> will probably come out.
> Tracy Crook
FWIW, the 93+FD owners have known this for years. Just a little air
screws up the cooling system performance big time. They even have
elaborate procedures to "burp" the systems to get rid of all air.
Sometimes it takes all afternoon to get all the air out of a system. And
these systems use an entrained air bubble remover 'swirl pot' as well to
vent out the bubbles before the system is connected to the overflow
tank. Of course the positions of all the components may have
necessitated some of the components. On the attached pic I put an arrow
pointing at the "swirl pot" (with the .9 bar cap). You can see the
tubing from the other pump cap to it. From the bottom of the swirl pot
additional tubes route to the expansion tank.
[Marc Wiese]
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