Overheating on 1994 Ford Explorer

I have a 1994 Ford Explorer. It overheated and shut off. I noticed the coolant would keep boiling over inside the coolant resevoir once the engine started heating up. What could be causing this. Could it be a blown head gasket?

Asked by for the 1994 Ford Explorer
Your Explorer has a 4.0L V6 OHV engine with a cast iron block and cast cylinder heads, so in theory and real life experience, the head gaskets are not known particularly for failure. That said, anything heated hot enough to the point it shut off can do anything. Such as crack the head. Did the temperature gauge go all the way up when this happened? Boiling in the coolant reservoir does not have to be from the presence of exhaust gases bubbling back, but can be. Have you checked the basics - thermostat, heat present inside the car, etc? Start there and then move on step by step from there. Does it smell like exhaust in the coolant reservoir? That is another tell tale sign of a cylinder head/head gasket failure.

Good luck.
2 more answers
Same exact situation. I replaced the egr sensor and valve and it ran fine but the radiator was bad too. Got so hot under the hood that the transmission fluid boiled out over the top. Simple fix but it's pretty confusing at first when you're trying to diagnose it because a lot of the same symptoms associated with a bad radiator or egr parts can also be a precursor to a rear main seal leak or a blown front seal.
I have a 94 explorer and had a similar problem it I replaced so many parts and after hundreds of dollars later it turned out to be the egr sensor