Not overheating, pushing water out overflow?

I have replaced the water pump, radiator, cooling fan assembly, fan sensor, thermostat and radiator cap. The car does not overheat but it over fills the overflow bottle and I lose fluid. I had bubbles with the radiator cap off and I thought it might be a head gasket, I put some head gasket repair in and then flushed it. The bubbles are gone but it still acts like it over heating. The temperature gauge does work.