The NAPA stuff is really a good buy. It is manufactured by Ashland Oil INC., makers of Valvoline. As for the Castrol mentioned earlier, yuck. I guess the multimillion dollar advertising they do has paid off. It is funny that Castrol uses base stocks for their synthetic oil that is not even as good as some manufacturers regular oil. They have also been investigated on their synthetic and synthetic blend oils. The problem is that the U.S. currently has no standards on requirements for oils to be called synthetic. I am in the oil changing business and can tell you that Castrol performs terribly when put to tests such as the V-block pin test, or the roller follower test, used when testing motor oils. You should see the damage under a microscope. Not good. Out on the west coast and some other areas Chevron actually manufacturers much of the base oils and it is blended and bottled by other manufacturers. It you research the history of oil development Chevron has been responsible for many of the breakthroughs like hydrocracking and isodewaxing. Pennzoil's pure base oil they advertised so heavy a few summers back was based on technology Chevron had in the 1980's. Also let me tell you that cheap oil is exactly that, cheap. Look at the ILSAC or API rating on that cheap stuff. It will not be current. The current rating is SL. It is surprising that some mass merchandisers have oil on their shelves that is manufactured using technology that is 30+ years old. Last year some of these oils were pulled off the shelf and tested and could not even pass the most basic quality testing. Stick with Valvoline, Chevron, Mobil, Shell, Havoline, Pennz or Quaker. For synthetic use Amsoil, Mobil 1, or Chevron. These are all good oils. Personally I use the Chevron Delo 15w-40 oil in all my rigs. It is approved for diesel or gasoline powered vehicles.
Sorry for the long post but I thought I should chime in on this one. This is not a plug for any of the manufacturers listed, just honest truth from someone who has grown up in the oil business.
