[FlatheadTed]

Water expands with heat ,Most flatheads will dump about a quret or so ,its a low pressure system . Once the water temperature rises excess water will need to go out a expansion tank will capture the water then as it cools it will suck it back in,which ever way you go you will be operating with a quart or so of less water .if your radiator is restricted a tank will help to push the water through as it then would be a closed system . the engine could operate hotter and not boil depending on the Thermostat and cap pressure .