A leaking headgasket can be classified as something external or internal. A leak can be identified as the external cooling fluid accumulates in the engine. The presence of liquid refrigerant can be detected by a black light on what appears to be an oil leak, the advent of refrigeration are shown in black light. External leaks can also occur as described above in the oil. Internal leakage can usually be diagnosed by excess fluid that accumulates in coolant expansion tank in the presence of hydrocarbons in the form of foam. For info about Ford Expedition repair don't hesitate to ask.