How Diesel Engine Oils Have Changed With Engine Designs

Over the past 20 years, regulators have constantly been mandating changes to on-road diesel engines (and diesel fuel) in an effort to reduce emissions. These changes inevitably necessitate a change in the composition of diesel engine oils. Case in point would be the dramatic changes that were mandated for the 2007 model year.

-Diesel fuel sulfur levels were dropped from 500 parts per million (ppm) to 15 ppm. Sulfur is a key component in the formation of exhaust particulates.
-Exhaust gas recirculation (EGR) rates were increased between 25 and 35%.
-Particulate filters were added to on-road diesel truck exhaust systems. The lower fuel sulfur levels and the resulting lower particulate formation were mandated not only for lower emissions, but also to prevent the contamination of the new particulate filters.
-These changes created new challenges for engine oil manufacturers. The increased EGR rates increased soot levels and created higher operating temperatures. As some anti-wear additives like sulfated ash and phosphorus can contribute to particulate filter contamination, a delicate balance had to struck between engine wear prevention and particulate filter preservation.
-The response to this new set of operating circumstances was the American Petroleum Institute (API) “CJ-4” diesel engine oil specification.

A new article on the main site entitled Diesel Oils Evolve With Diesel Engine Designs chronicles some of the changes that have occurred in the industry since the late 1980’s. We also showcase the AMSOIL Diesel Oil line and show how some products are a requirement for “2007 and later” trucks and how some oils are better suited to pre-2007 diesel units.