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    To visualize how oils compare, engineers use “spider graphs.” The spider web-like graphs have multiple linear axes along which results are plotted. Each axis represents a specific attribute. As attributes are added, axes are inserted accordingly. The further from the center zero point on each axis, the better the performance. Each new specification requires new tests, as shown here. Source: Chevron

For the first time in memory, two grades of oil for diesel engines are on the market. Should you purchase the older CI-4 Plus, the newer CJ-4 for engines with 2007 emissions controls, or stock both?

CJ-4 is designed to suspend soot and contamination in finer sizes and greater quantities than CI-4 Plus. It withstands heat better, improves wear protection, controls deposits, improves oil consumption, and has better soot-related viscosity control. But if you don't plan to add any 2007 vehicles to your fleet, the price differential would suggest staying with CI-4 Plus oil: CJ-4 costs about 20% more.

If and when 2007 on-road equipment comes in, you must run it on CJ-4 oil, which is formulated for engines produced after Jan. 1. These engines must meet the world's most stringent emissions controls to date.

What's The Difference?

When choosing oil, it helps to understand the difference between previous diesel engines and 2007 engines.

Maximum sulfur levels: Pre-2007 off-road engines can run on low-sulfur diesel (LSD) with 500 parts per million (ppm) sulfur (S500). But 2007 on-road engines must use ultra-low-sulfur diesel (ULSD) at maximum 15 ppm (S15).

In theory, S500 will be allowed for off-highway-only applications until 2010, but as a practical matter, most vendors are carrying only S15 ULSD.

Sulfur is an excellent lubricant, but it is a significant contributor to acid formulation in the combustion process. To neutralize acids in engines, oil contains alkaline compounds that convert to sulfated ash during combustion. Because sulfur levels are lower in CJ-4 oil, it needs less alkalinity, expressed as total base number, than oils used with 500 ppm diesel, S500.

Solids in the exhaust stream: This year's on-road engines use diesel particulate filters (DPFs) with diesel oxidation catalysts (DOCs) to control solids in the exhaust stream. The solids consist of soot and sulfated ash.

When sulfur contaminates its precious metals in the DOC (platinum, palladium, and others), it can't convert the soot to carbon dioxide. Soot and sulfated ash clog the pores and fill the passageways in the ceramic DPF. DOC contamination is the primary reason ULSD, or S15 diesel, has been mandated for 2007 engines. Previously, whatever solids entered the exhaust went directly to the air.

CJ-4 oils use “low SAPS” technology, meaning low sulfated ash, low phosphorous, and low sulfur. That's the oil, not the fuel.