Do I really need a coolant overflow tank?

This might help. http://forums.stangnet.com/showthread.php?t=582319

Cannoball888 said:

My car didn't have an overflow tank when I bought it, but the question is do I really need one? I understand that it will serve to catch excess fluid, but will it also serve as a container from which the radiator will draw fluid? If so, could someone explain how that works? Also, should the container be at a certain height in relation to the radiator?

Click to expand...

True, your car did not have a tank when it was new. If you have an original direct replacement cap you don't need one (unless you race at a track). When you superheat water past its boiling point which we do in our radiators by pressuring them (the more pressure, the higher we raise the water's boiling point) the coolant expands. In your car you leave about an inch between the top of the coolant and the top of the radiator. This space is filled by coolant when it gets hot and expands. On the coolant recovery systems, the radiator is filled right to the top all the time. The coolant in the tank will be pushed into the tank when hot and drawn back into the radiator when it cools. This way after the air in the system is expelled you never have to open the radiator cap again. You just maintain the coolant at the hot level in the tank.

Oh, and you want the tank's cap and radiator's cap to be as close as possible to each other in height.