A small truck company in the Imperial Valley (think El Centro, CA) just finished a study on engine oil. They hall produce out of the fields to processing centers. They use older trucks and just keep rebuilding them as needed. These trucks do not live a charmed life but work hard for a living. They use older diesel common engines and have a few off brands as well. Since their shop coordinates the rebuilding process with the mechanics and machine shop they decided to look into what might be the best oil for their situation. They decided that outsiders might not be of much help, no knowing their operation, that their expertise might better suit newer state of the art engine and not their antiques. These engines idle at a stop or creep along behind a tractor while being loaded and then make tracks back to the plant to unload and this is repeated over and over during the picking season, all day into the night and 7 days a week. And the winner is a diesel oil from ConocoPhillips, a HD Fleet Engine Oil, 20w-20. The claims have been less fuel used, lower over all temperatures by a 10-15 degrees and less wear on valve train components and less wear on engines with mechanical high pressure pumps. So, it appears that these old guys and these old trucks can learn new tricks and pick an oil based on performance instead of old habits.