API 1509 updated: New diesel engine oils will be licensed in January 2027
The American Petroleum Institute (API) has issued an updated standard that governs how engine oil marketers certify their gasoline and diesel engine oils to meet API’s stringent engine oil performance standards.
The 24th edition of API 1509, Engine Oil Licensing and Certification System (EOLCS), describes the voluntary API EOLCS. This standard:
- Outlines how new engine oil performance categories are developed;
- Establishes the requirements for licensing engine oils; and
- Defines the proper use of API certification marks.
In addition, the EOLCS details aftermarket conformance and enforcement procedures that help ensure products licensed as, or claiming to meet, API standards continue to deliver the performance they promise, providing confidence to oil marketers, OEMs, fleets and consumers alike.
API 1509 also provides the framework for introducing new engine oil categories, making it a critical component of the industry’s transition to API PC-12.
As the heavy-duty diesel market prepares for the new category, API 1509 outlines the licensing process, implementation requirements and quality assurance measures that help ensure PC-12 engine oils consistently meet the performance standards established through API’s collaborative standards development process.
By providing a transparent, standardized path from specification development to marketplace compliance, API 1509 helps support a smooth industry transition while maintaining confidence in licensed engine oils.
API PC-12 Engine Oils
API PC-12 (API CL-4 and FB-4) are being developed to ensure that heavy-duty diesel engine oils can keep pace with model year 2027 emissions requirements, and that the engine/aftertreatment designs needed to meet them — especially tighter NOx limits over a wider range of operating conditions, as well as longer useful life and extended emissions warranty expectations.
Benefits of the new engine oils
API CL-4 is intended to be backward compatible with API CK-4 while delivering stronger performance in areas such as oxidation, wear, aftertreatment protection and elastomer compatibility. Drivers and fleets should view CL-4 as the successor to CK-4 for both current and older engine technologies.
API FB-4 is intended to replace FA-4 and to enable lower-viscosity options (including xW-20) to support fuel economy in engines designed for it. Like today’s FA-4, FB-4 will be an OEM-application-specific oil rather than a universally backward-compatible category. Its main advantage is that it is designed to enable lower-viscosity options, including xW-20, for engines that use them.
From a cost-per-mile standpoint, the potential benefit is improved fuel economy, which can reduce operating costs over time.
Fleets will need to follow OEM recommendations carefully, because the benefit depends on using FB-4 in the right engine applications and avoiding misapplication in engines not designed for it.
Development of the API PC-12 engine oil category remains on schedule to support the EPA’s model year 2027 heavy-duty engine standards. API and industry stakeholders are advancing the required technical improvements to ensure the category is ready as planned.
While regulatory details may continue to evolve, PC-12 development is well underway and progressing on time to meet the needs of next-generation engines and emissions systems.
For more information about API 1509, PC-12 and API’s Engine Oil Licensing and Certification System, visit API.org/EOLCS.
Bill O’Ryan is director of the Engine Oil Licensing and Certification System (EOLCS) and Diesel Exhaust Fluid (DEF) Certification Programs at the American Petroleum Institute (API). He has worked in the transportation lubricants industry for over 30 years and joined the American Petroleum Institute (API) in 2022. His background includes additive package development, engine and driveline testing. Bill has oversight responsibility for the Aftermarket Audit Program (AMAP), an annual program in which thousands of engine oil and DEF samples are purchased in the marketplace around the globe and tested to ensure conformance with required specifications.
