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....
>
>
>
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