The Next Generation of Heavy Duty Oils
API PC-12 Advances Toward Finalization as Industry Prepares for 2027.
The development of the API Proposed Category 12 (PC-12) heavy-duty engine oil specification has entered its final stages, representing a significant milestone for the commercial vehicle industry as it prepares for the next generation of diesel engines.
PC-12 is being developed to support evolving engine technologies and regulatory requirements that will take effect beginning with the 2027 model year, ensuring that engine oils continue to play a critical role in performance, durability, and emissions compliance.
Formal request
This proposed category was initiated following a formal request from engine manufacturers in anticipation of the U.S. Environmental Protection Agency’s Clean Trucks regulations which outlined substantially tighter nitrogen oxides (NOx) limits, expanding the range of operating conditions under which engines must comply, and extend the useful life and emissions warranty periods. Collectively, these changes represent the most significant update to heavy-duty emissions requirements in more than two decades and necessitate corresponding advancements in engine oil performance.
To address these needs, PC-12 will introduce two new API service categories. API CL-4, the new “C” category, is intended to maintain backward compatibility with API CK-4 while delivering enhanced performance in key areas, including oxidation control, wear protection, after-treatment durability, and elastomer compatibility. API FB-4, the new “F” category, will replace API FA-4 and enable lower-viscosity oils, including SAE xW-20, to support fuel economy improvements in engines specifically designed for those oils.
Final balloting
The API Lubricants Standards Group recently approved both the PC-12 technical requirements, user language, and January 1, 2027 as the first licensing date for both CL-4 and FB-4. These elements are now proceeding through final balloting for incorporation into API 1509, marking an important step toward formal adoption of the specification following several years of coordinated work across ASTM, industry advisory panels, and the PC-12 New Category Development Team.
For fleets, PC-12 carries important operational considerations. While licensed PC-12 oils will not enter the marketplace until closer to 2027, preparation should begin well in advance. The introduction of two distinct categories, with differing compatibility and application profiles, will require fleets to understand how future OEM recommendations align with CL-4 and FB-4 and to plan accordingly.
API CL-4 is expected to serve as the primary successor to CK-4 for broad application across existing and future engines. FB-4, similar to FA-4 today, will remain application-specific and intended for use only where explicitly recommended by the engine manufacturer. As with prior category transitions, experience has shown that the most significant risks are operational in nature, including product identification, bulk storage management, labeling, and training, rather than formulation performance.
Facilitating readiness
To support a smooth transition, API’s licensing system will go live several months before the first license date, allowing oil marketers to enter products early and coordinate implementation with OEMs, fleets, and distributors. This early access is intended to facilitate industry readiness and minimize disruption as PC-12 enters the marketplace.
As PC-12 approaches completion, it underscores the continued collaboration required across the industry to ensure that engine oils change in step with regulatory, technological, and operational demands. For fleets facing increasingly stringent emissions requirements and longer equipment life expectations, PC-12 will be an essential element in supporting reliable, compliant, and efficient operations well beyond 2027.
