One goal of API CJ-4 was backward compatibility with the oil formulations of the older API CI-4 and CI-4 Plus classifications. However, the restriction in SAPS has resulted in a paradigm shift in engine oil technology. The reduction in ash levels from the norm of 1.3 percent to 1.5 percent to the mandatory maximum of 1.0 percent and the additional reduction in sulfur levels of the base oil and additives to 0.4 percent maximum will require replacing conventional metal-containing additive chemistries with alternative additive chemistries that are low in metallic content, sulfur and in some cases ashless.

The use of these alternative additive chemistries has reduced the engine oil's BN to a level ranging from 8 to 10. This lowering BN can reduce oil drain intervals in off-highway diesel engines that will still be allowed to use low sulfur diesel fuel (500 ppm maximum) till 2010. For on-highway diesel engines, this reduction in BN is not anticipated to affect current oil drain intervals because the use of ultra low sulfur diesel fuel (15 ppm maximum) will be the balancing factor in the oil drain interval equation. These factors could result in a differentiating of two different engine oils: one for off-highway diesel engines and the other for on-highway diesel engines (Figure 4) for the next few years. Further, it is anticipated that some OEMs will require BN minimums depending upon the application their engines are used in.

CJ-4 can be used with the 500 ppm sulfur fuel to be used in off-road diesel from 2007 to 2010, but there may be a reduction in oil drain intervals from previous oils.

To meet the API CJ-4 limit of 0.12 percent phosphorus, the amount of ZDTP used in the formulation of heavy-duty diesel engine oils has been reduced. This reduction in ZDTP will require the use of alternative ashless antiwear agents to protect the valve train from wear.

The reduction in sulfur levels to 0.4 percent maximum along with the NOACK volatility limits of 13 percent maximum and the need for increased oxidation stability due to the increased thermal stress placed on the engine oil from the use of heavy EGR rates and aftertreatment have resulted in an increased use of Group II, Group III and Group IV basestocks.

Figure 5. Future Engine Technology 2010