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Engineers use spider graphs like this to compare the characteristics of oil.

If you haven't yet negotiated your lube oil contract for 2007, you'll soon discover that you'll be making decisions you never faced before. For example, Should you buy CI-4 Plus or CJ-4 as your engine oil, or should you stock both?

For the first time in memory, two grades of diesel engine oils will be available from most suppliers. Previously, new diesel oil formulations were “backward compatible” and improved. This meant they could be used instead of any previous formulation with increased performance in almost every respect, and the preceding grade of oil quickly disappeared.

The oil developed for engines with 2007 emissions controls is different. So much has changed that CJ-4 uses different chemical technologies. And because CJ-4 is different, most suppliers will continue to provide the older CI-4 Plus for the foreseeable future.

To decide which oil is right for your fleet, you need to understand the differences. To help visualize how oils compare, engineers use spider graphs. They're called spider graphs because they resemble spider webs. These comparative tools have multiple linear axes, along which results are plotted. The further from the center zero point, the better the performance. Each new specification adds new tests, as shown in the illustration.

Engines produced after Jan. 1, 2007, must meet the world's most stringent emissions controls to date. They will get even tighter in 2010 when another new oil will be available. The most obvious differences between current diesels and 2007 engines are:

1. 2007 on-road engines must use ultra-low sulfur diesel (ULSD) with a maximum of 15 parts-per-million (ppm) sulfur. Today's engines run on low sulfur diesel (LSD) at 500 ppm. Sulfur is an excellent lubricant, but as an impurity, it is a significant contributor to acid formulation in the combustion process. It also contaminates emissions-reduction equipment.

To neutralize acids in engines, oil contains alkaline compounds that convert to sulfated ash during combustion.

2. 2007 on-road engines will need diesel particulate filters (DPFs) with diesel oxidation catalysts (DOCs) to control solids in the exhaust stream. The solids consist of soot and sulfated ash mentioned above. When sulfur contaminates its precious metal, a DOC 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.

Because sulfur levels are lower, CJ-4 oil needs less alkalinity, expressed as total base number (TBN), than oils used with 500 ppm diesel, S500. CJ-4 oils use “Low SAPS” technology, meaning low sulfated ash, low phosphorous and, low sulfur. That's the oil, not the fuel.

Producers' fleets

But there's another factor that clouds the stocking decision. Mixers, dump trucks, and diesel pickups are all on-highway vehicles, but many concrete producers also operate a variety of off-highway and stationary diesels. Non-highway engines are now allowed a diesel fuel that contains up to 5000 ppm sulfur. Sulfur levels for non-road equipment will drop to 500 ppm in June 2007, but will not be required to meet S15 standards until June 2010.