[joegr]

Head gasket problems on the 3.9 are incredibly rare. Cooling system problems with symptoms that seem a lot like a head gasket problem are very common. The plastic parts, including the degas bottle, rot and crack. The cracks are so small that you don't see them and you won't see the coolant leaking. However, air will get sucked into the cooling system and cause the engine to overheat. It looks a lot like a head gasket problem, but it isn't.