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Group II and Group III oils

Base oils made with the Iso-DeWaxing process are called Group II, and are significantly more pure and have higher performance than Group I base oils. Chevron Delo 400, Mobil Delvac 1300, and Shell Rotella are made from pure Group II oils. Motor oils made with Group-II base oils leave far fewer wax and tar deposits in your engine, and have much better low and high temperature performance than Group I oils. The resulting oils are roughly 97% good stuff (oil) and 3% bad stuff (paraffin and wax). We just cut that 12" dinner candle down to about 2½".

The high and low temperature performance of oils are described by the Viscosity Index. The VI tells us how much the oil thins out as it gets hot. Oils with higher VIs maintain their viscosity better at high temperatures. If the VI is 90 to 100, we call it Group II; if it's refined to a VI of 110 to 115 we call it Group IIa. In the late '90s, an even more involved process was invented yielding base oils with VIs over 120. These base oils are called Group III or "unconventional base oils." The higher the VI, the fewer additives are necessary to achieve the required viscosity. For example fewer additives are needed to turn a Group III base oil into 10w-40 than are required for Group II base oils. Group III oils have essentially no paraffin and wax in them, at least as compared to the 12" dinner candle per gallon in Group I oils.

Group III oils have properties approaching or equaling synthetics, so long as the temperature is above about 40°. Group III based oils are often claimed to not perform as well as synthetics in a couple ways: their low temperature performance is not nearly as good, it is sometimes claimed on the basis of the "ball bearing test" that they offer lower impact resistance, and since their flash point is slightly lower it is claimed that they burn off more easily. However, most modern engines are water-cooled, so it's hard to see how the slightly better flash points of the synthetics ever come into play. I personally don't make a habit of dropping a handful of ball bearing into my oil pan, so I'm not completely clear on what the impact tests mean to me. The low temperature performance of the Group III oils can be improved enormously by blending in a relatively small amount of synthetic base stock and other additives.

Since about 2000, it has become possible at moderate extra cost to process Group II and Group III oils so that their performance below 32° nearly matches the performance of traditional synthetics. Because of this, the oil companies found they could now produce relatively inexpensive 5w-30 and 0w-20 oils. Car companies were quick to see that such oils would help reduce the fuel consumption of their vehicles by a percent or so, which is important as Detroit finds themselves selling more trucks than cars. So, these "fuel-efficient" oils are quickly becoming the factory recommendation in most cars. It's not at all clear that these new low- viscosity oils lead to the longest engine life, but it is clear that these oils help the car companies meet their CAFE federally- mandated fuel economy standards.

In the late 1990s, Castrol started selling an oil made from Group III base oil and called it SynTec Full Synthetic. Mobil sued Castrol, asserting that this oil was not synthetic, but simply a highly refined petroleum oil, and therefore it was false advertising to call it synthetic. In 1999, Mobil lost their lawsuit. It was decided that the word "synthetic" was a marketing term and referred to properties, not to production methods or ingredients. Castrol continues to make SynTec out of Group III base oils, that is highly purified mineral oil with most all of the cockroach bits removed.

Shortly after Mobil lost their lawsuit, most oil companies started reformulating their synthetic oils to use Group III base stocks instead of PAOs or diester stocks as their primary component. Most of the "synthetic oil" you can buy today is actually mostly made of this highly-distilled and purified dino-juice called Group III oil. Group III base oils cost about half as much as the synthetics. By using a blend of mostly Group III oils and a smaller amount of "true" synthetics, the oil companies can produce a product that has nearly the same properties as the "true" synthetics, and nearly the same cost as the Group III oil. The much more expensive traditional synthetics are now available in their pure forms only in more expensive and harder to obtain oils. To the best of my knowledge, Delvac-1, AMSOil, Redline, and Motul 5100 are the only oils made from pure traditional synthetics.