I am thinking its the head gasket but just want some input. My GF just got her car bacck from the shop about a month ago she had to have a new distributor (before I knew her). The car ran fine for a couple of weeks then it just overheated on her at highway speeds on the way home from work. Since then it overheats. Its usually good for a day or two with her driving back and forth to work (about 50 miles). I have checked the fans (and seen them operate), changed the thermostat and the coolant sensor(thought it might not be turning the fan on soon enough). Last night I went out and bleed the system again for about a hour it ran without overheating. What I did notice and why I think its a head gasket is the bleeder would always have air bubbling out even after the hour. I also noticed if I gave the motor a quick rev (nothing crazy just a little punch) the coolant would either come up out of the radiator or if I had the cap on would shoot into the overflow. So what I am thinking is after a day or so over normal driving the coolant is being pushed out of the system and it overheats. There is no white smoke or water in the oil.