Reply to "Overflow tank"

did I miss something, I see you are now calling it an expansion tank. the fill volume for an expansion tank would be different than overflow tank. Like I state on engineering forums, I need to see a drawing about what you are asking.

a TRUE expansion tank will not need a catch tank as it will maintain a pressurized air volume above the coolant.

IF the cold volume of air is twice the coolant expansion volume, when it is compress with expanding coolant it will have the pressure at 15 psig. thus I was looking at filling the converted overflow tank 7" low at cold.

If the cold air volume is between 2 and 1 the coolant expansion, the pressure will increase to 15 psig at a temp less than 195F AND some air will be blown out of a 15 PSIG relief cap.

I have also considered making the overflow tank into a pump suction header tank, then this tank would be filled, and with the least increase in temp, the "solid" cooolant's pressure will quickly go to 15 psig and a quart recovery tank is needed