What would cause pressure in the cooling system fluid backs into overflow till it overflows and the is no heat 1998 windstar 3.0L already replaced thermostat and water pump?

you must purge th system you have a air lock allow the vecile to run with the rad cap off till it get warm the shut it down till it cools add collant you may have to do this a few times........rosdale joe The way I did it was to fill up my radiator, then turn the car on. When its getting to the normal temperature is when it starts to pour water to the reservoir.... at this point you turn your heater on on high and the neddle to the hot possition... this should bleed the cooling system. Also check the preasure on you radiator cap.... the [problem on my car was the radiator cap.