How many gallons is the capacity for the cooling system of a Ford E250 Van with a 6 cylinder 4.7 engine with air?

For a ( 1996 ) Ford E-250 :

4.9L / 300 cubic inch inline six cylinder engine , automatic transmission , air conditioning

The engine cooling system capacity is ( 18.0 U.S. quarts , includes heater )

It came from the factory with a 50 / 50 mix of distilled water and GREEN color antifreeze meeting Ford specification ESE-M97B44-A