Lumina engine overheating

[buick century]

I replaced the original engine with a Lumina engina

After 6 months it has started overheating. Needle goes to 3/4 of the temperature gauge. I rush to stop the car ASAP.

Have rewired the fans to run at full speed all the time
Have changed the water pump.
Has blown the radiator tank, the water hose, and the radiator "engine coolant low" indicator sensor.
Have replaced the radiator cap (16 lbs).

Excesive pressure in the water, boils into the water bottle leaving the radiador with less water, causing to overheat even further..
Ambient temperature is around the 95 degrees in Miami.

Any suggestions short of changing the engine?

[tri-power]

Have you checked the thermostat? You might want to go to a low temp thermostat so it will circulat coolant out of the engine sooner. There is a possibility of an air bubble in the system, however you have Had this problem before and after you replaced the water pump so the chances are slim. Have you checked for blockage on the radiator causing poor circulation? Have you had the system flushed to remove any contaminants in the system? Is the enginr block clean and free of dirt and other foriegn matter? Remember if the motor has a lot of dirt or such, it acts as an insulator and reduces the ability of the air around it to cool it off.