I have a 96 mustang GT with a 4.6 ltr V8, the car has not been severely overheated, but did overheat once a few months prior to this issue when the heater hose fitting popped out of the Carbon Fiber (Plastic) Intake Manifold. I repaired this issue. A few months later out of the blue the engine oil light comes on, So I pull over and chk the oil, its way low & barely showing on the dip stick. I add 2.5 qrts of oil and bring it up to the full mark and drive home - no problems. Keep in mind, the engine runs good and strong and no overheating issues. the very next day - i take the car for a Job interview and on the way there, the oil light comes on again just as I arrive, so I pop the hood and immediately notice the milky oil coming out of my radiator over flow tank, chk the oil and its nearly empty again. I know what the possible causes are, what is baffling me is that I have never seen a blown HD put oil in the coolant, its always been just opposite with the coolant in the oil. in this case there is no coolant in the oil and the re is no milky residue in the valve covers. additionally - the engine still runs Tits, no hesitation or misfires, etc. Are there any other possible reasons for oil to be pumping into my coolant other then Damaged Head or Block &/or Blown Head gasket..??
If it has an engine oil cooler that is cooled by the engine coolant, then it's possible that it is leaking there.
The leak must be after the oil pump for the oil to be at a higher pressure than the coolant, for the oil to be pushed into the coolant and not the other way around.
I would probably guess at the head gasket leaking following the overheating incident, but it is worth looking for easier fixes first.
check if the engine temperature is normal,secondly find out if the vehicle has hard start in the morning, thirdly find out the level of engine oil if is getting low. Automatically the there is a leakage between the water pass-way and oil pas way on the cylinder head . or the cylinder head is warped/ bent you may need new gasket and refacing both cylinder head and engine block.