I have a 92 Ford Explorer with 4L engine and 175, 000 miles on it. I have recently experienced the car overheating. The coolant keeps bubbling out of the overflow container. I have filled the radiator twice now with coolant, but each time it over heats. Typically, when I get into traffic after about 20 min. Of driving. I did drive it 15 miles at 60mph and the temperature guage stayed on the cool side, but when I stopped, the guage needle slowly moved to the hot side. I have ran the A/C each time, if that matters.