If you or your company owns 2007 or 2008 diesel pick-ups or “on-road” heavy-duty diesel trucks, you may be wondering why the truck manufacturer is so adamant about using motor oil that meets the American Petroleum Institute (API) “CJ-4” specification in the engine. You may be wondering if you can “get by” with a motor oil that does not show this designation on the label. The answer is NO! You cannot “get by” with a diesel engine oil meeting the older API “CI-4” or “CI-4 PLUS” specifications in these engines. If you try, there’s a good chance that expensive damage will be the outcome.

How did this whole thing begin? Prior to a few years, the U.S. The Environmental Protection Agency (EPA) decided to impose stringent new emission limits beginning with the 2007 model year for on-road diesel engines used in heavy-duty and pickup truck applications. This would reduce the quantity of nitrogen oxide and debris released by the exhaust pipe. The EPA found that these new vehicles would reduce harmful pollution by 95% when combined with engine redesign, ultra-low-sulfur diesel (ULSD) fuel, and new engine oil technology.

The addition of exhaust after-treatment devices and increased exhaust gas recirculation (EGR) rates are the two most significant changes to the engines. These two modifications necessitated developing a diesel engine oil using a completely new methodology.

The exhaust after-treatment devices being used are “diesel particulate filters”. In order to produce much cleaner emissions, these particulate filters remove soot from the exhaust. By burning it off at high operating temperatures, the accumulated particulate matter is removed from the filter. Diesel engine oils from earlier generations contained additives that could clog or harm particulate filters. Strict limits on the amounts of phosphorus, sulfur, and sulfated ash are present in the new CJ-4 engine oils. In addition to being very expensive to clean or replace, a plugged or damaged particulate filter can significantly reduce fuel economy due to increased back pressure.

Another significant change required by the EPA was a 97% reduction in diesel fuel’s sulfur content. The sulfur content of diesel fuel for on-road use was reduced from 500 parts per million (ppm) to 15 ppm starting in September 2006. The purpose of this was to prevent fuel from harming the brand-new exhaust after-treatment components. Many people were concerned about this because sulfur was an essential additive that kept fuel pumps and injectors lubricated. The fuel companies were not required to use a different ingredient to lubricate the injectors and pumps in place of the sulfur. In order to delay the wear of your diesel fuel’s pump and injectors, it is a good idea to add an aftermarket fuel additive. All diesel engines running on ULSD fuel would benefit from doing this. A fuel system lubrication additive should be compatible with exhaust particulate filters and ULSD fuel, as well as being designed to provide that lubrication.

The removal of nitrogen oxide is done by increasing exhaust gas recirculation (EGR) rates by as much as 35%, with the exhaust filter handling the removal of particulate matter from the emission. EGR systems return some of the exhaust gases to the engine that would otherwise be released through the exhaust pipe. This rate increase raises operating temperatures, produces more soot and acids, and increases emissions. Another justification for the significant modifications made to the CJ-4 specification’s design was this. The engine oil must have increased heat resistance, a larger dispersant package to handle the increased soot levels, and increased depositing and oxidation prevention capabilities due to these new hostile operating conditions. Additionally, CJ-4 oils are less volatile, which makes them more palatable.

The best performance and protection for post-2007 diesel engines will be provided by CJ-4 oils. To remove the nuisance of fleets having to stock different diesel motor oils for trucks built before and after the 2007 model year, CJ-4 oils are designed to be “backwards compatible” with pre-2007 diesel engines. Only one CJ-4 diesel motor oil can be kept on hand by fleet owners to service all of their diesel trucks.

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