As diesel engine builders hustle to meet stringent new emission standards for 2027, they have again asked for new lubricants to help them meet the challenges, and that means new standards for diesel engine oils. The current standards set for engines entering service in 2017 — CK4 and FA4 — will be replaced.

Jeffrey Harmening, senior manager of the Engine Oil Licensing and Certification System within the American Petroleum Institute, says API’s Lubricants Group has established a team to begin the test development phase of the PC-12 diesel engine oil category.

“The PC-11 category produced today’s familiar CK4 and FA4 engine oils, and the PC-12 project will take a similar path with a target date for licensing oils under new ratings and having them on the shelves by Jan. 1, 2027,” he explains. 

“In the meantime, API, the OEMs and other stakeholders in the process must develop tests and specifications for the new lubricants and adjust any existing tests used on previous categories that can be applied to the PC-12 project,” he explains. 

Engine OEMs petitioned API in March 2021 for a motor oil category including the following improvements over CK4 and FA4 lubricants:

  • Increased oxidation performance
  • Wear test capabilities
  • Lower viscosities to meet 2027 model year fuel economy standards in EPA and California Air Resources Board regulations.
  • Improved exhaust stream after-treatment capabilities.
  • Improved compatibility with the latest elastomers used in modern engine seals and gaskets.

Harmening says there will be another “C” category oil, but it has yet to be determined if it will follow with a “CL” moniker. 

“Sometimes letters are skipped in the naming of new oil categories,” he says. “Whatever the rating letters are, however, the new “C” oil will be backward compatible, so older engines rated under earlier “C” categories will still be covered with the new formulation.

“Things could be different for the “F” category, which will come out of the PC-12 project,” he explains. 

“This category is not required to be backward compatible, and whether the FA4 oil will be carried forward with the new “F” oil remains to be seen. Currently the new category is being seen as an all-out replacement for FA4 because of demands for lower viscosity as far down as XW20.”

Harmening says it’s unlikely the new “F” rating will greatly affect farm equipment, since the more stringent demands for increased fuel economy are aimed primarily at over-the-road transportation equipment. 

Because government regulations tend to creep over time, however, and with improved fuel economy as a “top of the mind” regulatory tool to reduce carbon emissions with bureaucrats on both sides of the Atlantic, those building diesels for the global agricultural market likely will be watching trends. 

This round of development of new lubricant categories faces increasing challenges in the laboratory, Harmening explains.

“Much of the old Mack T-11 and Mack T-12 hardware (engines and accessories) for tests are coming to the end of their useful lives,” he says. 

Engines used in test labs with specific fuels and specific oils under a variety of loads, speeds and other challenges are torn down and inspected for wear. Before additional tests can be run, new engines and hardware must be available.

“The desire of API and other testing facilities is to find replacement tests that will satisfy the older C categories,” Harmening explains. 

“We will be able to carry over several tests from the PC-11 development into the PC-12 project, but we will have to evaluate each for limits imposed by the new requirements,” he says. 

“The lower WX20 viscosity for on-highway diesels is just part of a trend to meet new emission requirements, and that will continue as designers try to squeeze as much efficiency out of engines as possible by lowering internal friction and drag produced within the oiling system.”

He says the committee will also be establishing protocols in the PC-12 project for the Detroit Diesel scuffing test, as well as Ford’s valve train wear tests.

Harmening says many OEMs, marketers, additive companies, and oil blenders already have been meeting since March 2021 to plan the PC-12 project and, beginning in January 2022, began working on specifications and standards in earnest. 

“The 2027 deadline is aggressive, but those involved agree they’ll be able to deliver the category as requested,” he says. 

That means, in December 2026 or on New Year’s Day, 2027, there will be a new API diesel engine oil category and CK4 and FA4 will step down as the latest standards.