Please help! I have an 03 Grand Am 3400 that continues to run hot. Over a period of time I have replaced the exhaust manifold gasket, head gasket, timing cover gasket, water pump, and now the thermostat, coolant sensor, and radiator. After replacing the radiator, coolant sensor, and thermostat, I refilled the system (it only allowed 1/2 gal of coolant. I started the car an let it come to operating temp. Still could not add more coolant. I opened the bleeder screw but it never ran coolant. After 45min I started to hear a knocking sound near or from the thermostat housing almost like the sound of positive pressure engaging then release pressure. After a few more minutes the temperature red lined and the car started to over flow from the reservoir. Also cycled the heat in and off once car came to temp. Why is this happening?