When it comes to motor oil, no matter who slaps their label on it, the oil itself and the additive packages most often come from oil refineries. Most oil refineries are owned by third parties, and have little to no affiliation with the various companies that purchase their oil (except for a business affiliation). Thus the difference between Yamalube oil and Evinrude oil, if the two were purchased from the same oil refinery, might not be all that significant. However, one difference between the various brands of motor oil is the additives. The additives are what make different formulations of oil work better in certain kinds of engines. While some motor oil brands will purchase additive packages from the refineries that are quite similar if not identical to the competition, the big name brands, like Yamaha and Evinrude, often have their own special additives. These additives maximize the oil’s effectiveness in the Yamaha or Evinrude engines.
It’s important to be aware of the brand of oil in the engine, and not just stick in any motor oil that seems to work well. The effects of using one motor oil over another will manifest over time, and using the right oil will prolong the life of the engine.