I would like to know more about the overheating problem. When you checked the coolant was it low?

Even if it was not I think it was an excellent suggestion to pressure test the cooling system before replacing a bunch of stuff. Before I had that done I would have the system professionally flushed to get as much as of that--how to screw up a cooling system and not plug the leak crap, out. Armed with the results, I would start make cooling system decisions from there. I suspect the copper turd was for the cooling system only.

You mentioned evidence of water in the oil. What and how much evidence? The first place I would look for evidence of a blown head gasket would be oil in the water rather than water in the oil. Oil in the water looks like a foamy chocolate shake.

In your case evidence of water in the oil it may be a collection of condensation from sitting so long. Sitting that long, even with no evidence of water in the oil, I would change the oil and filter ASAP, cheap safety measure.

If you are concerned about the head do the suggested leak down test first. FYI--each cylinder must be at top dead center when tested. If one or more is bad, I would check the torque on the head before removing it so I knew if I needed to address that aspect before the head gasket is replaced. As suggested, I wouldn't replace the head gasket without having the head checked thoroughly beforehand.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas