The 5W20 Ford "recommends", is only on cars sold in USA. The same engines in Australia, use 5w30. The use of 5w20 is for a lower CAFE(fuel mileage) average. On most cars, it amounts to a fraction of a mile, per gallon. My 2000 4.6l oil cap says "use 5w30". The 2001 model and up say 5w20. I doubt Ford re-engineered the 4.6l, between years. In fact Ford released a TSB, that 5w20 is OK, for use in 5w30 engines. However, When I used 5w20, I noticed, I was 1/2 quart down after 600mi, with some smoke at start up. When I switched back, no smoke and 1/2 quart low at 1000mi. The 5W is oil viscosity at cold start up. The 20/30 is when hot, the higher being slightly thicker. A thinner oil will, get by worn seals, much easier. I called the Mobil tech line for more info. They claim 5w20, recommended, but 5w30, 0w30 and 0w20 all would be acceptable.