[curtis73]

One of several things could be happening, and I think that the above responses are all valid. Its quite possible that the stock radiator wasn't effective enough in the first place, but you can do things to help.

If everything is new or in perfect operating order, you can try changing the antifreeze mix from 50/50 to 70/30 (more water) to help cooling in the summer. Adding water wetter or another surfactant will help keep the water in contact with the surfaces of the water jacket and help cooling. Using a smaller water pump pulley will do two things; speed up the water pump and speed up the fan (if its a belt-driven fan).

But, anything could be wrong with any part. The water pump could be eroded and not pumping well. The fan clutch may not be engaging. The radiator may have crusty corrosion inside. The thermostat may be sticking closed. The internal passages of the water jacket may be excessively rusty. The fins in the radiator might be bent over.

You may not have any room to go bigger size with the radiator, but usually you can go thicker. If your current radiator is a 2-row, see if one of the many aftermarket companies makes a 3-row. If all else fails, you can have a radiator shop build you one to fit your needs. You can also add a helper fan (as has been mentioned) or maybe an aftermarket hi-flow belt driven fan.

Whatever you do, don't try to fix it with a lower-temp thermostat. That won't do any good.