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API Approves PC-12 Diesel Engine Oil Category

Fleets and drivers should expect improved performance of oils which supports the enhanced durability of engines, and aids in meeting regulations, says API.


API Lubricants Group announced it voted to establish a New Category Development Team to begin the test development phase of the PC-12 Diesel Engine Oil Category. 

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The Engine Manufacturers Association made a request to the Diesel Engine Oil Advisory Panel (DEOAP) in March which established a New Category Evaluation Team (NCET) to evaluate the request. The NCET voted this week to recommend to the DEOAP to proceed with the development of Proposed Category — PC-12. During the ASTM D2 meetings in Anaheim, Calif., the DEOAP approved the recommendation to establish a New Category Development Team (NCDT). API Lubricants Group considered this request and voted to establish the NCDT, officially kicking off the test development phase of PC-12.

The new category is being requested with the following improvements:

  • Increased oxidation performance
  • New wear test capability 
  • Addition of lower viscosities
  • Improved aftertreatment capability 
  • Expansion of elastomer compatibility

Engine test obsolescence (test hardware becoming unavailable) will also be considered. The T-11 and T-12 are test are not likely available for PC-12. The Category Life Oversight Group (CLOG) will continue to assist with technical evaluation and statistical support for correlations where appropriate. The NCDT will develop a T-11 replacement as needed.


Request for first licensing date from API is no later than January 1, 2027. This coincides with the anticipated 2027 implementation date for EPA and CARB HD on-highway regulations. The recommendation requests to consider December 1, 2026 as the date for first license. This is similar to the PC-11 licensing timeline which resulted in API CK-4 and FA-4.

Potential benefits to diesel engines include the following:

  • Enables new engine technologies that are expected to experience higher brake mean effective pressure (BMEP) and customer demands, as well as accommodate anticipated regulatory requirements of extended useful life and warranty periods.
  • Supports requirements for fuel economy for certain engine models.
  • Supports new elastomers used in modern engines.

Fleets and drivers should expect improved performance of oils which supports the enhanced durability of engines, and aids in meeting regulations. This can result in reduced cost of ownership.


Potential environmental benefits include limited SAPS (Sulfated Ash, Phosphorus, Sulphur) will support engines that satisfy tighter environmental regulations on lower emissions. Longer oil drain intervals may be possible which support sustainability goals.

The current C subcategory will maintain its backward compatibility and the new F subcategory is intended to replace FA-4 and does not need to retain backwards compatibility. The potential for existing engine tests becoming obsolete will be addressed as needed.