Save on inventory costs by using the same oil, CJ-4 or CI-4/SN, in both gasoline and diesel engines.
Save on inventory costs by using the same oil, CJ-4 or CI-4/SN, in both gasoline and diesel engines.

Before the 1900s, we used to change CD- and CE-classified diesel oils every 8000 to 12,000 miles in Class 7 and 8 trucks and more often for smaller ones. We did “dry” maintenance (chassis lubrication only) halfway between “wet” intervals. Since then, fleet managers and mechanics have adjusted their routines to keep up with many advances in engine oils and truck technology.

Most improvements in oil formulations have followed changes in emissions regulations. While major oil refiners periodically upgrade their products to remain competitive, establishing new standards drives real progress. ASTM and the American Petroleum Institute (API) continue to set higher performance standards for motor oils.

New classifications—CH-4, CI-4, CJ-4, and more—reflect the most recent industry strategies for emissions. The C stands for compression ignition (diesel), the following letter indicates its place in the progression, and the number specifies use in four-stroke cycle engines.

When the EPA implemented its 2004 emission standard to reduce nitrogen oxides (NOx) 15 months early in 2002, CI-4 oil was ready to control heavier soot loadings produced by exhaust gas recirculation (EGR) technology. Shortly after its introduction, CI-4 was found to fall short of what was actually needed to meet the 2004 standard. CI-4 Plus took its place, with the same tests but modified requirements.

The next advancement in 2007 was introducing diesel particulate filters to control particulate matter, consisting primarily of soot and metallic ash. CJ-4 was developed to minimize ash formation and to suspend increasingly finer soot particles, thereby reducing filter plugging. (See sidebar.)

For 2010, EPA further reduced the levels of NOx and particulate matter. Both CJ-4 and CI-4 Plus oils are considered current by API.

Some oils engineered primarily for diesel use also can be used in gasoline engines. The API Service Symbol, or the “donut,” indicates the service appropriate for the oil. If it is marked “CJ-4, CI-4/SN,” it can be used for all vehicles. That cuts inventory, at least for gasoline and medium-duty diesel engines that both can use 10W-30 oil. You also can use 15W-40 in gasoline engines, however fuel economy will suffer slightly.

High-tech equipment

In addition to advanced formulations, new computer controls in trucks have extended oil service life. Faster computers allow precision timing of multiple fuel injection pulses, which improves mileage and results in more complete combustion and less soot.

If you change oil and perform preventive maintenance according to manufacturers' recommendations, your routine need not change. But if you determine your oil drain schedule using oil analysis, and follow the American Trucking Associations' Technology and Maintenance Council Recommended Practices for determining proper change intervals (RP 334 for heavy duty and RP 1403 for light and medium duty), you must repeat the exercise if you change API service classifications.

For many fleets, the easy way to manage oil drains is to use the latest oil, CJ-4, and follow engine makers' recommendations. But for larger fleets, where savings can quickly build, managers are re-examining these practices.

A&A Ready Mixed Concrete's Southern California 700-truck operation has 22 EPA 2007 or EPA 2010 trucks. To avoid confusion, the entire shop uses CJ-4 oil. The Northern California fleet has no newer trucks, so they still use CI-4 Plus.

“We do oil analysis on each truck at least once a year,” says Michael Kurzman, fleet manager for the Long Beach producer. “Our older Macks would easily go 35,000 miles between oil drains. When a truck would accidentally miss an interval, analysis showed the oil would still be good-to-go at 70,000 miles. The new MP7 engines perform well, but oil analysis indicated that with the new emissions technologies, drain intervals had to be reduced.”

Controlling Emissions: Equipment vs. Oil

Specially formulated oils have been developed to work with emission-controlling truck equipment, and reduce pollutants from exhaust. But fleet managers who invest in exhaust after-treatment systems may save money by using more basic oil.

CJ-4 oil is formulated to extend the life of diesel particulate filters and to reduce catalyst poisoning and soot loadings. Lower-priced CI-4 Plus oils can be used in the engines, but they may shorten filter cleaning intervals and catalyst life.

Navistar addressed EPA's 2010 regulations with Advanced EGR (exhaust gas recirculation), augmenting a proven technology with more precise computer control of fuel delivery. Even though more EGR was applied, better combustion limited soot formation, so no new oil was needed.

All other manufacturers adopted an exhaust after-treatment, called selective catalytic reduction (SCR). This NOx-reducing process takes place outside the engine in the exhaust system, requiring no change in oil formulation. Because this after-treatment allows reduced EGR, many fleets are using less costly CI-4 Plus in post-2010 engines.

Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Associations and is on the board of the Truck Writers of North America. E-mail

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