John, unless you have someother problem, I think a pressure cap would be needed. For every pound pressure you put on your system, you raise the boiling point by two and a half degrees and especially if you are in a high elevation, the water will boil at a lower temp also. If you are running a fan clutch, that could be a problem or if your fan is too far from the radiator or if the fan shroud has been removed could cause over-heating.
Truck Tinker
