I would say it is probably headgaskets. It is possible for head gaskets to leak in to exhaust ports and not make its way in to the oil. Which would cause the coolant to overheat rapidly. It is simple to test. Go the an autoparts store and buy a kit to test the coolant for carbons. Simply remove the radiator cap, start the engine, put the tool where the radiator cap goes on the radiator. The tool has fluid in it and will change color if you headgaskets are leaking. It tests for exhaust fumes in the coolant.
