My friend has a 2002 F150 with the 4.6 and he is still looking for a motor oil. I'm trying to help him decide if Mobil 1 0w20 or 5w30 is best. His manuel says to use only 5w20 and anything else will void the warranty. Does Mobil 1 0w20 meet Fords warranty that calls for 5w20? Or should he just stick with the Motorcraft 5w20 semi-synthetic that the book says to use? Thanks for any help!