1992 Ford Tempo

Engine Cooling problem
1992 Ford Tempo 4 cyl Two Wheel Drive Automatic 180000 miles

My car has been over heating for a couple of weeks now. I have been adding coolant/water every time I leave to go somewhere. I t started out running hot. I added more coolant and it seemed to help. Now it overheats unless I constantly keep adding the water. The over flow container stays full, but the radiator will be almost completely empty. I can only assume that the over flow is not emptying back into the radiator as there is no indication of a radiator leak. Can this be a thermostat problem or water pump problem or what else? Also how would I go about remedying this poblem.
August 15, 2009.

Need to pressure check coolant system for leaks
have to check and locate what is leaking

Aug 15, 2009.