Did you refill just the reservoir or did you also fill the radiator? The engine block will be full of air that has to bleed out as you refill the system. That will take about two gallons of coolant. If you have a 318 c.I. That usually occurs by itself but if the thermostat is sealing really well you are going to have to help it or wait a while for the air to bleed through it. Until that happens the thermostat will not open and the engine will overheat. Thermostats open in response to hot liquid, not hot air.
If the radiator is full to the top but you haven't gotten enough coolant in yet, look for the sending unit for the temperature gauge on the dash. It is screwed into the intake manifold very close to the thermostat housing. That's at the end of the upper radiator hose. It will have a single purple wire plugged onto it. Unplug it and unscrew it. As I recall, I think it will take a 1/2" deep socket. As soon as it's removed you'll see the coolant level in the radiator go down. Add coolant until it runs out of that hole, then reinstall the sensor.
Monday, April 8th, 2013 AT 9:55 PM