Hey guys i know its not a mustang but i figured since its a ford you guys may be able to help me out. Anyway i have a very weird overheating problem with my 2001 Ranger 3.0 liter. It only happens about one time per one tank of gas, so 95% of the time it runs fine. Whats happens is, it gets to operating temp and stays there for a while, then out of nowhere my heat blows cold. The temp guage will then drop a bit and seconds later it skyrockets up to the point where it overheats. By the time i try and pull over to shut it off, the temp drops back down to normal. I have replaced the thermostat and radiator cap thinking it might be the problem but no luck. I have also bled the system of air and it has fresh coolant in it. All of the hoses appear to be fine also. Something weird i have noticed also is that the overflow tank does not have a vent, so the whole cooling system is not vented. I need your guys help to figure this out!!! It has made me late to class a few times and is getting very irratating!! Thanks!!!