Bill Freeman wrote:

                          BIG SNIP

What you are saying Jeff is there have been about two  million rotary

Mazda's made

with lots of air in the coolant and it was pumped and cooled like crap. I

find that

a bit hard to swallow. No stock Mazda that I know about has a separator tank.
Here is a picture of a second gen RX7 13B pressure cap on the thermostat

housing

and rad return pipe. Exactly like my modified pump except mine is about
four inches lower. I think you are forgetting the idle mode. When the

engine idles

the flow is very low and the bubbles get a chance to rise to the high spot
and go out the pressure cap valve to the overflow tank.

Paul Lamar

Paul,

I think that the radiator top tank becomes the separator for the typical
car.  Esp (as you so correctly pointed out) at idle.  I think the difference
that Jeff is talking about is a system with a radiator which is not at the
highest
point in the system at the top tank filler cap.

This is why auto systems are designed this way, to dump out air.  If you
build a system with a different type and location of cooler, expect trouble
if you don't have a big enough section at the highest point to get the flow
rate way down.  I suspect that a 3"- 4" diameter section or so would slow
the flow enough to get separation of air.  If the cap is here and an overflow
tank is used, you will have an air separator.

Bill

In the first gen RX7, like the one I just bought for Robin, the rad is indeed the
highest
point and the pressure cap is on the rad tank. In the second gen the 
thermostat housing/water pump return pipe holds the pressure cap as shown
in the picture. That is higher than the rad tank. The ID of the pipe is the same as 
the return hose to the rad. A short section of larger pipe could easily
be plumped in here in some airplanes. In my KIS cruiser and Lancairs
it would be a problem with cowl clearance.

Paul Lamar
 
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