JFB is right - most of the expansion is maintained in the expansion tank.
When I was stabilizing my cooling systtem, I had a catch tank that was connected to the radiator cap.
It would cycle about a coffeecup worth of fluid back and forth between a hot, and cold engine. See this thread, third post down.
http://pantera.infopop.cc/eve/...62/m/6401013256/p/11
Anyway - If your "catch tank" holds twice that much, it seems to me you would have margin, and if you put in 2 Quart sized tank, you would never have to worry about spillage.
Rocky
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