My 91 Explorer is loosing coolant as well but I can't tell where its going. It seemed to first come up when I had the radiator hoses replaced about a month ago. The overflow bottle looks fine when its running but after it cools down the fluid seems to be being sucked back into the radiator so it goes down by a cup or two everyday or so. Its not overheating, there is never anything on the ground anywhere at home or work, there is no antifreeze in the oil, pressure test holds about 16 lbs.,gas check for CO2 in the antifreeze was negative,I just replaced the radiator cap,the heatercore isn't leaking inside the car, its not coming out the exhaust and theres no white smoke and the thermostat is about a year old.
I do have leaving valve cover gaskets although they've been like this for a while. Could this have something to do with it? My mechanic is stumped, he mentioned possibly either an air pocket at or near the heatercore or a bad thermostat--anyone have any other suggestions--I'm open for just about anything right now!!!
Barry
91 Explorer Sport
174,000 miles