2005 Mitsubishi Magna radiator

Sounds like you have a pinhole leak in the radiator. Check with some place like Autozone or O'Reilly's about renting or borrowing a cooling system pressure tester and pump the system up to about 18 PSI. While you're there, pick up a cooling system leak detector kit consisting of a flourescent dye and black light. You should be able to borrow the light also. Add the dye to the coolant and drive for awhile. Pop the hood and slowly move the flourescent light around. The leak will stand out worse than a sore thumb with the dye.