There isn't a 100% sure way to test that I know of. There are only 3 main ways where the oil can get to the coolant. 1. Thru the head gasket. 2. Thru the timing cover gasket. 3. Thru the oil cooler. I wouldn't think anything is cracked because you would have the opposite, coolant in the oil. Oil pressure is higher than coolant pressure. Those coolers have an outer steel tube that is filled with coolant. Running inside this tube, thru the coolant is a dozen or so smal copper tubes that carry the oil and cool it. What happens is the copper slowly erodes and springs little leaks. 40 psi oil gets into the 12ish psi coolant. I personally have never seen a bad head gasket on 7.3, unless it was all done up and lifting heads. Or, a bad timing cover gasket. Ford used that gray silicone that sticks like a mother in combination with o-ring gaskets.I myself would go to the weakest link first and go for the cooler. Hope this helps!


Oh by the way. I just saw in the for sale section in here, a '94 engine that a guy is parting out. Don't know any of the details, but if you're want to get out of it cheaper you could give that a try.

ok i talked to guy at the shop and he said that he can rebuild mine with new gaskets and that should fix it. is it the copper tubing or the gaskets that usually leaks?

Check the compression on the motor if can, I bought a '92 idi some years back and thought the same thing, having already replaced the cooler on my '87 bought it right up for 500 only to find out it was a cylinder sleeve cracked. But to answer your question replace the entire cooler.