The current API CK-4 and FA-4 diesel engine oil specifications were introduced in 2016 and split the existing diesel engine oil category into two separate categories. This was driven by changes in engine technology to meet emissions, renewable fuel and fuel economy standards for reduced CO2 and other greenhouse gas emissions.

API CK-4 oils succeeded CJ-4 engine oils and are backward compatible diesel oils. Backward compatible means CK-4 may be used where CJ-4, CI-4, CI-4 PLUS and earlier service categories are recommended. API FA-4, on the other hand, was new and intended for engines beginning with the 2017 model year.

Last year, the Engine Manufacturers Association (EMA) requested that a new diesel engine oil category be developed to meet the needs of future engines. The Diesel Engine Oil Advisory Panel (DEOAP) then established a New Category Evaluation Team (NCET) to consider the request and subsequently recommended to the American Petroleum Institute (API) to move forward with the development of Proposed Category - PC-12. The API Lubricants Standards Group voted in December to establish the New Category Development Team (NCDT) which officially began the test development phase of PC-12.

Karin Haumann, OEM Technical Services Manager for Shell Global Solutions, was the chairperson for the NCET and will serve in the same role for the NCDT. The NCDT manages the development of new API Diesel Engine Oil Service Categories. This includes working with all interested parties to identify areas of increased performance that will enable engine manufacturers to meet the changing NOx emission standards expected in 2027 and requirements for fuel economy for certain engine models.

The new category is being requested with the following improvements:

  • Increased oxidation performance
  • New wear test capability
  • Addition of lower oil viscosities to include xW-20 in the F subcategory
  • Improved aftertreatment capability
  • Expansion of engine elastomer compatibility

With engine technology changing, several engine tests used to evaluate engine oils are expected to become obsolete due to diminishing engine hardware supplies. Several replacement engine tests will need to be developed.

The current C subcategory will maintain its backwards compatibility and the new F subcategory is intended to replace FA-4 and does not need to retain backwards compatibility.

The request for the first licensing date from API is no later than January 1, 2027. This corresponds with the anticipated 2027 implementation date for EPA and CARB HD on-highway regulations. The recommendation from API is to consider December 1, 2026, as the date for first license of engine oils meeting the standards of the new category.