It’s been said here before, but it’s worth saying again. 20W oils are CAFE driven and have nothing to do with engine protection or bearing clearances. The cost to manufacturers for failure to meet CAFÉ are HUGE. Go to NHSTA’s website and see for yourself. For example, a manufacturer who fails to meet the CAFÉ requirement of 20.7 MPG average for light trucks pays a serious penalty. Missing the 20.7 MPG requirement by just 0.1 MPG (20.6MPG) will cost a manufacturer of 400,000 trucks $2.2M in penalties ($5.50 per vehicle per 0.1 MPG under the CAFÉ requirement).
Ford’s case proves what it’s all about. They wanted to use it to help meet CAFÉ. The EPA said OK as long as you 1) Ensure customers use it, 2) Make sure it’s readily available, and 3) You demonstrate it’s actually being used through oil sale numbers. So Ford not only recommends it (if not actually requiring it) for nearly all it’s new engines, but goes even further and makes the recommendation retroactive back 7+ years on many older vehicles to help sell the oil.
The oil may be fine in some engines. It may even be great in a few others. But when you combine the fact that it’s current recommendation was born in an attempt to meet CAFÉ fuel economy standards, with the lack of any manufacturer claiming the oil provides engine protection superior to existing oils, there is little reason for the individual interested in maximum engine protection to use it.
It’s recommended for my Ranger, and I’ve used it. It seems to work fine, especially in the winter. But in the summer, I can’t tell any difference in fuel economy between Motorcraft 5W20 and Mobil 1 5W30. Good 30 weight oils have a proven track record with regard to engine protection. Is there any evidence that a good 20 weight offers engine protection superior to a good 30 weight for summer use? If not, and if there is no significant difference in fuel mileage, what’s the benefit to anyone other than the manufacturer?