Once a dose of air gets to the pump, it matters not at all how much water is elsewhere. It stops moving.
The pump will not reprime without outside help. So, small bits of air must be removed (even during flight) so that they do not become large bits of air sitting still in front of the pump. The system goes through large volume changes with RPM and temperature changes. So you can tap into the highest part of the system where air is likely to collect, and run a small line to the bottom of a pressure bottle that has your pressure control cap mounted. Keep this bottle about 1/3 full of coolant. Keep the line to it small in diameter so volume changes will move unwanted air quickly to the bottom of the pressure bottle. There the bubbles pop to the top of the bottle. Any volume reduction in the system can now only recover coolant, not air.
I have this system since 1980. It works like magic. Not my idea. It was on every RX-2 and RX-3 in America.
It may take several heat cycles to get all of the air out. The first will be most impressive with most of the coolant missing from the bottle.
Lynn E. Hanover
In a message dated 5/2/2008 9:06:55 AM Pacific Daylight Time, bob@bob-white.com writes:
Hi Lynn,
I had to sleep on that advice to get it straight in my head. I believe
it's good advice, but could still be connected in a detrimental way.
It's important to feed the water pump from the bottom of one of the
coolers. If the coolers are in series, the outlet and inlet would both
be on the bottom with a straight connection between the top fittings
connected together. That would simplify the plumbing as well as insure
that in the event of a cooling leak, the second core would remain full
of water at least until the first core was nearly empty. Using the top
fittings for outlet and inlet would still make one of them flow bottom
to top, but would be detrimental if there were a loss of fluid.