I have replaced the radiator on my 00 LS, 3.4 liter. Also, I have replaced the radiator cap, radiator hoses, water pump, and thermostat. The engine runs hot when the system is pressurized. When the pressure is released, the temp runs normal. I have bled the system until I get hot air out the heater. I drive the car and the system will run hot again and loose the hot air from the heater. The cooling system is not loosing any fluid and there is no indication of fluid being mixed with the oil. Does anyone know what else can be done to fix this problem.