Wow, I would have thought Ford woul have resolved this problem years ago. It was a common problem when the first aluminum block engines came out. Back in 1963 Buick made a small aluminum block V8 that was put into their Buick Specials (small/mid size car like the Tempest and Olds F85) Later they had a lot of cooling issues because the aluminum block was not compatible with the cast iron heads. The coolant produced an electrolitic action that started eat at the aluminum and corroding the cooling passages.
This happens when certain metals are exposed to the same liquid (coolant) with an electric current present (engines are grounded as part of the electical system). This is the same process used to electro plate metals with zinc, gold, copper, nickel and chrome, etc. This problem was solved back in the 1960's with special additives to the coolant, and later with using different alloys in the aluminum block, and not using incompatible metals that contact the coolant.
I certainly would have thought that Ford would have enough forethought to not run into this same old problem again???
...Rich