I think this is a new one, why does Ford reccomend 5W-30 for the 4.6L motors, but 5W-20 for the 5.4L motors? Sorry to come out of left field on this one, but I searched and couldn't find an answer, just a random question, trying to gain some new knowledge.

Thanks for any responses.
-Andrew

 

They don't. As far as I know, every new vehicle (with the exception of the new Shelby, that's speced for 5w-50 full synthetic) comes with a factory fill of Motorcraft 5w-20. The older 4.6's and 5.4's (and a bunch of other engines for that matter) were speced for 5w-30, but at some point around 2002, they started specing 5w-20 and they back-speced most everything else for 5w-20 as well. There is a TSB out there that lists all the years and engines that are back-speced.