I remember seeing that on the Ford Taurus too. And now that you mention it, I do not think that I have ever seen 5-20 sold anywhere. Maybe it is a dealer-only item, and is another way for Ford to make money by having their dealerships be the only supplier for the 1 recommended oil for the car.
By the way, does anyone know where I can find Mobil 1 0-40. I am currently in Daytona Beach and see 0-30 everywhere, but cannot find 0-40.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record