Group I is no longer used, very basic oil.
Group II is your common regular “dino” or petroleum oil. Group II works just fine as we spoke of but does not have the benefits of synthetic oil
Group III is your typical “synthetic oil.” However, it is actually a refined product of Group II. That is, it has been filtered and treated to be a superb quality of oil. However it is still subject to the shearing or molecular instability of its ancestor group II oil. Don’t expect this oil to run 10,000 or even 15,000 miles. Some do last this long, because of additives, but once they wear out the oil basically falls apart. It is not a true synthetic. Its is often referred to as “hydrocracked.”
Most oils that claim to be synthetic are not. This includes almost every synthetic, Casrtol Syn-Tec, Pennzoil Platinum, Wal-Mart synthetic, and the list goes on. Why is this allowed when it is not synthetic? Mobile 1 discovered in the early ‘90s that Costrol’s full Syn-Tec oil was actually Group III, or a filtered Group II. Mobile 1 sued Castrol saying that it was not what it claimed to be. Castrol defended by saying that the oil was not Group II because it had been altered to a point to where it was reasonably the same as Mobile 1. After Castrol won, most oil companies switched over to the cheaper Group III synthetic and most of the consumers never did and never will know it. Recently there has been debate about whether or not Mobile 1 is still fully synthetic, such debate is speculative and nothing has been confirmed. Mobile 1 Extended Performance is still fully synthetic for sure.
http://theoildrop.server101.com/foru...0&fpart=1&vc=1
http://theoildrop.server101.com/foru...rue#Post860829
Group IV oil is manufactured from non-petroleum ingredients in a lab. It is not naturally occurring in any way. Often referred to as PAO oil or Poly-Alpha-Olefin. These are true synthetics; this is where it is at! However, how much better they are than group III is debatable, but group IIIs are fakes.
Group IV, or real synthetic oils, have smaller molecules and are all the same size and usually smaller. Being smaller offers the advantages of not being to large to move through tolerances and thus avoids being sheared or broken into smaller pieces. Additionally, it allows the molecules to move around and over each other more easily, which can contribute to better viscosity and lubrication.
Group IV synthetics include Royal Purple, Mobile 1 Extended Performance, and Amsoil (not Xl-7500), their are others but these are the most popular.
Group V oils are rare, and not usually used for automotive base oil. The only example I know of is Redline oil, which is made from polyester and ester, better known as plastic clothing. As scary as that sounds it is probably the highest quality oil you could by, but that doesn’t mean the best oil. Usually used as an additive when making lower group oils.
Synthetic Blends
This is petroleum oil mixed with synthetic oil. Basically it helps the oil maintain its viscosity at extreme temperatures. Plus it makes for good marketing and profit.