5W20 is used to decrease oil pumping losses in the engine to help maximize efficiency to effect minimum fuel mileage requirements mandated by fed gov.
The 0WX grades are thin, thin, thin at low temps and will pump up and through a cold-start system very rapidly, a good thing.
I won't try to bypass Ford engineers; they know what they're doing, but everything is a compromise. For my comfort I'd start using 0W30 or 5W30 full synthetic. Every bit of information I've seen dealing with engine longevity indicates use of the slightly heavier grade of oil for best service life.