Chuck,

The purpose of the pressurized cooling system is to raise the boiling point of the coolant and allow the system to run at a higher temp.

Any problem with the radiator such as your leak or plugged tubes or fins would create a overheating problem. Your problem is inadequate operating temperature...the other end of the spectrum.

The one and only device on a car that is designed to bring that temperature UP is the thermostat. With the gasket in the housing, the thermostat should be held firm between the two halves of the housing. If the housing is all corroded, which it sometimes is, and coolant can pass through somehow, the system is defeated and it's a pot luck deal.

Good luck and keep us in the loop on your progress.

Stuart