Found some interesting info in this article regarding tank sizing.
https://www.cumminspower.com/www/lit...30_p93-115.pdf
We all know coolant expands when it warms up but an actual number wasn't readily available....at least to me. It seems that 6-7% of system volume is generally accepted as volume required for expansion. That is for an overflow tank or a degas tank.
A degas tank should have a volume of 17% of the total system. 6% for the above mentioned expansion and 11% for coolant. They call it draw down capacity on page 95.
So lets assume 4 gallons of coolant in the system, not counting the tank. 17% of that is 2.7 qts, I like round numbers so 3 qts it is. 3 qts is approximately 175 cubic inches and that would be the proper size for a degas bottle/surge tank.
Right?.....