Here are the API oil group categories taken directly from Chevrons website
Group I+: Still high sulfur and low saturates, but processing conditions have been adjusted to make higher VI. This higher VI, in the range of 100-105, gives better cold cranking and Noack performance, enabling these base oils to be used in 10W-30 engine oils with minimal Group III or Group II+ correction fluids. Examples are special products from Marathon Ashland and Valero. Making these type of oils reduces base oil yield, so they may cost more than standard Group I.
Group II+: Adjusting processing conditions, several refineries can make these oils with 110-120 VI. This enables significantly improved CCS and volatility, making it possible to blend 5W-20 and 5W-30 GF-3 and GF-4 engine oils using these oils without any correction fluids. As with Group I+, the extra quality costs more to produce.
Group III+: Not available yet commercially. These will be available in the second half of this decade made from gas to liquid processes. They will have VI's exceeding 140 and will be used for 0W-XX and 5W-XX engine oils and super-premium transmission fluids.
What are the drivers behind GF-4?
The simple answers are tougher Emissions and Fuel Economy standards mandated by the U. S. Government. Automotive OEM's need better fuel economy to meet Corporate Average Fuel Economy (CAFÉ) limits. They also need their catalytic converters to provide reduced emissions for 120,000 miles. Higher quality base oils are an important part of the solution to GF-4.
Why does fuel economy affect the base oil blend?
Fuel Economy is measured by an engine test, the Sequence VIB. In order to pass this test, blenders may need to go to lower viscosity base oil blends, but still must meet the volatility limit of less than 15 Noack. In general, this requires a higher VI base oil blend.
Why do emission regulations impact lubricants?
There is no engine test that measures emission system stability, but the OEM's have data showing that sulfur and phosphorus are poisons for catalytic converters and must be limited. Thus, in GF-4 oils sulfur is limited to 0.5%, maximum, in 0W- and 5W- engine oils and 0.7%, maximum in 10W- engine oils. Phosphorus is limited to 0.08%. This restricts the amount of zinc dialkyldithiophosphate, the workhorse anti-oxidant and anti-wear agent, which can be used in engine oils, which in turn, may restrict the amount of Group I oil in GF-4 blends.
Is there enough Group II base oil available to meet the needs of GF-4?
Yes. According to National Petroleum Refiners Association (NPRA) data, in North America, there are over 80,000 barrels per day of capacity to make Group II, Group II+ and Group III base oils.
Why was Group II+ base oil developed?
Chevron produced the first Group II+ base oil commercially in 1998. It is the most cost effective base oil for 5W-20 and 5W-30 passenger car engine oils of GF-3 quality. Group II+ has higher VI, which translates to improved (low-temperature) cold cranking performance and lower volatility. The cold cranking performance of a 5W-XX engine oil is measured at -30°C using a Cold Crank Simulator, and the volatility of the engine oil is measured using the Noack Test, which simulates oil evaporation in an engine-like environment.
At our Richmond, California refinery, we make Chevron 5R, a high-purity Group II+ base oil with optimized viscometric properties and volatility for making 5W-XX engine oils. There are now four producers of Group II+ in North America. Properties of all of our base oils can be found on our website: Group II / II+ Base Oils Typical Properties Table.
What about 10W-30? For GF-4, can it still be made with Group I base oils? What are Correction Fluids?
Most Group I base oils cannot be used for GF-4 10W-30 without some help. Higher VI base oils, called correction fluids, can provide this help. Depending on the properties of the Group I oil used, the final blend might require 10-50% of a correction fluid, such as 5R. If a Group III correction fluid is used, less will be required.
Another problem with Group I oils is that they have higher concentrations of impurities, such as aromatic compounds, and sulfur and nitrogen compounds. These impurities accelerate oxidative degradation. So, in addition to needing help with viscometrics and volatility, Group I oils need help to meeting the requirements of oxidation tests, like the Sequence IIIG engine test. Therefore finished lubricants formulated with Group I base oils formulations require boosted additive packages to achieve similar performance to engine oils blended with Group II.
While it is possible to blend GF-4 10W-30 using mostly Group I base stock meeting spec will require more expensive correction fluids and more expensive additive packages. Factoring in the added cost of correction fluids, additives and increased blending complexity total formulating costs is comparable between Group I and Group II base oils, but the issues, such as tankage and product handling, will make the total formulated costs come out pretty much the same.
What about the new ATF specifications, DEXRON-IIIH?
Transmissions are becoming more complex and more compact as cars become more streamlined, so transmissions are running hotter. By 2004, most service fill ATF will need to meet DEXRON-IIIH specifications.
A good Group II base oil, like Chevron 100R, is the most efficient path for meeting DEXRON-IIIH ATF specifications. Eventually, Service-fill will move completely to synthetic quality.
What about synthetics? Will synthetic base oils be widely available?
Almost all synthetic-quality lubricants can be blended with Group III base oil, a much more cost effective alternative to expensive PAOs. We see steady growth in these premium lubricant markets, especially in automotive lubricants. This growth will take off, when natural-gas-derived base oils become available, towards the end of this decade. These gas-to-liquid (GTL) base oils will be super Group III oils. They are already they are being called Group III+ by many in the industry.
Currently, there is plenty of good-quality Group III available in North America to meet expected demands for the next several years. Among the highest quality Group IIIs available are Chevron 4R and 7R.
