True, water expands when it gets hot, but not much. Four percent to be exact at 200F. The capacity of 1949 engine and radiator is 15 quarts, which becomes 15.6 quarts at 200F.
However, as soon as water reaches its boiling point, it expands rapidly, and the weakest part of your cooling system will blow. The pressure cap on the radiator is designed to blow first. If it's not working the radiator will split.
Keep in mind that water boils at different temperatures depending on conditions. The higher the elevation, the lower the boiling point. The more antifreeze you use, the higher the boiling point. Finally, the higher the pressure, the higher the boiling point. Modern cars/trucks have higher ratings on pressure caps to increase the boiling point of the coolant.
