1995 Chrysler LHS over heating

Engine problem
1995 Chrysler LHS 6 cyl Wheel Drive Type unknown Automatic 104, 00 miles

My car was running fine with no problems and then all of a sudden it over heated. We replaced the thermostat and thought that was the problem it did not fix it. I drove the car approx 4 miles down the road after it ran in the garage for 25-30 min going down the road I noticed the heater would blow out hot air and then it would blow cold and then back to hot air. The check engine light hasnt come on since we replaced the thermostat but the gauge goes up to hot. We have not drove the car since then. When the car overheats the water comes from the overflow for the radiator.