You guys are really confusing me!  Granted all my rotary work so far is on my car.  Once upon a time, my car had an AST (air separator tank).  It was a small round job next to the radiator, maybe 3 inches OD, 3 or 4 inches tall.  I’m thinking it served similar purposes to the swirl tank in your designs?  Mazda made it of plastic and it had a nasty tendency to burst after aging in the heat soaked engine bay long enough.  Most Rx-7 owners including myself, removed the AST system - others replaced it with aftermarket aluminum versions.  As I recall it had a tube at the bottom that went downwards to an extra nipple on the bottom of the radiator, but I forget where the input came from.  I am wondering how this system compares to the ones you are describing?  Where is the pump in the last figure (Steve vs Jeff)?  And where is the “airbleed hose” bleeding air from?  Is the idea that it is just a high point in the system that continuously is drawing out any air bubbles that get created or trapped in the system?

I have to ask another related question - why not use Evans waterless coolant?  I think we discussed it a bit before.  It seems like the expansion/contraction is a lot smaller because it boils at a much higher temperature than standard coolant/water mix.  I run this in my car now, but my car is a project car that hasn’t gotten enough serious abuse to have more opinions on the efficacy of Evans.  But I believe that Rotax engines use it - so aircraft use is not beyond the pale.  I am just wondering if all this (seeming) complexity in the cooling system arrangement would be needed if a waterless coolant were used.

— James