Snake;
To answer your question a faulty radiator cap can create the problems you described. Water boils at different temperatures depending on the pressure it is under. A radiator cap rated at 15 pounds will raise the boiling point approximately 30 degrees. As the water temp rises the pressure increases. Once the pressure in the cooling system exceeds the caps ability to hold the pressure the water is expelled into the over flow. When the pressure in the cooling system drops a vacuum is created that pulls the water from the overflow back into the radiator. With a faulty cap you end up with 2 issues. First coolant that should be in the radiator is pushed into the overflow as the motor heats up. Second the lack of pressure in the cooling system lowers the boiling point. The faulty cap will not let the engine draw the overflow water back into the radiator as the engine cools. This gives you a low coolant situation as well as an area for air bubbles to form above the cooling fins. All this combined will cause the car to run hotter than normal. I would say you have fixed the issue.
~Michael
