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A new category of oil, American Petroleum Institute (API) CJ-4, will be required for the '07 on-road diesel engines to meet the needs of after-treatment devices, such as diesel particulate filters. "These filters will be sensitive to fuel and lubricant byproducts," says Mark Betner, Citgo.

In the quest to make the lubricants compatible with after-treatment devices, a major breakthrough was accomplished. "This upgrade to the CJ-4 specification is probably the biggest advancement in engine oils in years," says Dan Arcy, Shell Oil. "Some of the improvements are in the areas of wear protection, high-temperature oxidation stability, deposit control and soot handling."

These advancements resulted from new formulation requirements. "This is the first time there have really been chemical restrictions put on the oil," says Arcy. These limits are 1.0% ash, 0.4% sulfur, 0.12% phosphorus and 13% volatility. "Just to put that into perspective, CI-4 Plus oils are between 1.3% and 1.5% ash."

"These chemical limits have been imposed in order to make the lubricant compatible with after-treatment devices," says Reginald Dias, director, commercial products, ConocoPhillips, 76 Lubricants. The resulting compounds have a lower total base number (TBN) than the previous CI-4 Plus oils. The TBN measures the ability to neutralize acids formed in the oil.

"The 1.0% maximum sulfated ash limit caps the allowable detergent level, which will limit the fresh oil TBN of some API CJ-4 formulations and prevent the use of very high TBN oils," says Mark Betner, Citgo.