Sorry Al, I think you are incorrect on the no vapor theory.  While it is
true that in many big three cooling solutions the level in the overflow
reservoir will change as the engine is cycled from cold to hot back to cold
again,  the cooling system is never all liquid.  There has to be vapor
before you start.  I am sure that we both agree on the following points: An
automobile cooling system needs to be pressurized to operate above the
boiling point of water.  You can't have pressure without a spring in a
closed system.  The spring used is compressed vapor.  If you don't start out
with vapor, you will push out coolant until you create some vapor, this
vapour is the result of coolant that has boiled in the block somewhere.  A
rad cap is a pressure relief device not an accumulator; it is open or
closed.  For a spring loaded to opperate as an accumulator you need an
unlimited supply of coolant/air/oil/etc. to flow through at a rate high
enough that you can create back pressure, much like the spring loaded
pressure regulator on an engine lubrication system.

Your radiator may look like it is full but the filler neck likely extends
down past the top of the tank or it is on the side of in the case of a cross
flow radiator, either way the cooling system is not 100% liquid filled.

Since we are all building hybrid cooling systems, we need to remember to
leave some vapour in the system ( as you are doing ) to make sure that we
are operating with a pressurized system "before" we start to expel coolant
from the system.

George mentioned the fact that a good many vehicles have systems that never
vent coolant through the cap unless over heating, I would agree with him
that this is the best solution; usually it involves a combination expansion
tank / swirl pot and a pressure cap that is vented to the ground. Cheers -
Ian


-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]On
Behalf Of al p wick
Sent: Sunday, June 26, 2005 8:02 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Coolant Leak


Actually, I think the opposite is true. I understand the auto approach is
to NOT have any air in the cooling system. I don't recall the details of
their reasoning. In my experience, the safety advantage of cup-o-air is
much more significant.
BTW, it's probably more like 2 cups. The goal is to have enough air
cushion to prevent pressure from reaching cap rating. When you include
coolant temp, fluid level, and pressure info, it really improves your
understanding of how your system is behaving.

If you ever open your car radiator and find air at top, it indicates a
problem with your cooling system.



-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html



On Sun, 26 Jun 2005 13:15:14 -0400 "Ian Dewhirst" <ianddsl@magma.ca>
writes:
> Al, your experience with the value of having an air cushion is
> supported by
> every automotive cooling system that I have ever seen (many).
> Typically
> autos use either a pressure cap and expansion tank that is not
> filled to the
> top, or an overflow bottle into which coolant is expelled and
> recovered.  I
> get the impression that some people assume that these overflow style
> systems
> contain no vapour when cold, I don't think that assumption is
> correct.  The
> overflow systems all have expansion capacity built into the top of
> the
> radiator, or some other part of the cooling system they are never
> completely
> filled with coolant.  The bigger the cooling system the greater the
> volume
> of vapour stored cold.
>
> -- Ian
>
> (GM, Chrysler, and Ford are not trying to piss you off with those
> side
> mounted radiator caps.. ;-)
>
>
>
>
> -----Original Message-----
> From: Rotary motors in aircraft
> [mailto:flyrotary@lancaironline.net]On
> Behalf Of al p wick
> Sent: Sunday, June 26, 2005 11:58 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Coolant Leak
>
>
> My focus is on flight safety. I found great value to having appx. 1
> cup
> of air at the top of my cooling system....
>
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>
>

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