I don't think this is the death knell of thin oils. Rather, they are the future.
I think this is an example of the penny pinchers and number crunchers at Ford over-riding the decision made by engineers and designers. As was suspected, they needed CAFE points and this was an easy way to both get those mpg points, and , ultimately, sell more cars. I think it is more evidence that we need to be our own advocates, our own researchers, and that blindly following the rec of a manufacturer comes with its own set of perils and caveats.
I have a buddy who runs a local repo operation and he runs F450s with Triton V10s. Has had 4 trucks cease up from piston scoring over a relatively short period...all of which were replaced under warranty by the dealer. They still force him to use 5w-20 (Penz Plat in this case) to keep the warranty on the new engines...even though the head mechanic at one of the largest/busiest Ford dealers in the state reported after tear-down of the last engine (he did all 4 engines) that it was likely a lack of MOFT combined with elevated oil temps during short bursts of full throttle activity after long periods of idling in hot weather.
Everything with a grain of salt, mind you. For engines which were designed to use 5w-20 from the outset, it's likely just fine. However, even then we see Coyote and Voodoo V8s that call for 5w-50 for track use....which is not that much harder than aggressive stop-and-go driving.
But, the lesson here is that these ford modular engines were designed with 5w-30 in mind (with the manual even permitting 5w-40 and 10w-40 for severe use in hot environs)....and then they were back spec'd to the thinner oil. Virtually nothing mechanical about the engines was changed; the bearing geometries were the same, as were the piston skirts/oil jets, as was the oil pump and the oil coolers (if optioned).
