0-20 is def not necessary, 5-20 is OEM, correct. I typically use 5-20, but if I can get 0-20 cheap, I see no harm in using it, esp if full synthetic. I won't put in 5w-30 though, unless the PDS matches very closely with or betters the Motorcraft 5-20 Syn Blend PDS. Even though the label on synthetics says the weightage, not all oils are same in their characteristics, weightage being the same.