1997 F53 460 and Rotella R6 5w40

lenr wrote:
Everyone should use the oil that provides the best night's sleep. However, here is a link to a technical article on why diesel oil in a gasoline engine might not be a good idea.
http://www.machinerylubrication.com/Read/28576/comparing-gasoline-diesel-engine-oils-

To answer the original OP question, I would would use Motorcraft 5W-30 Semi-Synthetic or Mobil 1 5W-30 Full Synthetic, both for gasoline engines unless oil consumption is excessive, which might call for thicker oil.

From memory (I'm not going to cite a reference):

Ford and Honda did some research back before the turn of the century that showed that thin oil on cold startup was more important than thick oil when up to full temperature in terms of long term wear. My late 90s and 00s Ford gas engines recommended 5W-20 for this reason. (Have not owned a Ford gas engine since 2004 so have no knowledge if this has changed.)

Back even earlier GM found that increasing the polymers in the oil to move it from 10W-30 to 10W-40 caused their engines to develop more carbon deposits. (Modern engine design might have found another fix for this, but it could also be why Ford goes with thinner oil--The modular engines had a tough time with carbon.)

Quote:

Not only does 5W40 Rotella T6 meet API SM specifications (oil for gasoline engines), but it's sold as mixed-fleet oil which means it's specifically intended to simplify fleet maintenance by using it in both gasoline and diesel engines.