sounds a bit like you need to back flush the cooling system due to a blockage / severe restriction. ie the water circulates in one direction around the cooling system, so disconnect and remove the thermosat. Disconnect a suitable cooling hose and blast the complete system with a garden / water hose and be amased at the gunge that comes out. Make sure the car interior heater si turned up high (hot). Also check that your radiater is not blocked by 'road kill' plastic bags etc. Make sure you replace the coolant WITH anti freeze, replace the thermostat, and tighten up hoses and connections - not too tight...
WotNotAgain, March 2009