On a 1995 ford falcon cooling system does the filler cap have any other function other than adding coolant.?

that cap serves a few different purposes. for one thing ever pound of pressure held on coolant will increase its boiling point 3 degrees(not 14.5) the cap maintains this pressure, if it gets too high a little will be released to the overflow tank. when the engine cools off, pressure will drop ,and as the liquid actually takes up less space in the radiator, it will allow more of that coolant to return form that very same tank. in that cap you will find two valves and three seals.