The American Petroleum Institute (API) is the key authority when it comes to developing engine oil standards for both heavy-duty diesel and passenger vehicles. These standards are designed not only to ensure safe and effective engine performance, but also to keep pace with evolving technology, emission regulations, and design improvements in engine manufacturing.
The API is currently preparing to launch its next-generation engine oil standard: Proposed Category 12 (PC-12). Set to be officially licensed in early 2027, PC-12 engine oils are poised to replace today’s heavy-duty categories and introduce new formulations capable of protecting advanced engines, improving sustainability, and reducing long-term fleet costs. Now is the time for diesel mechanics and fleet managers to get informed and prepare for the coming shift.
What Are PC-12 Engine Oil Requirements?
This new API diesel engine oil classification is being created to meet emission regulations and performance expectations that will go into effect alongside the 2027 model year engines.
The primary goals of PC-12 include:
- Dramatic Emission Reductions: The PC-12 standards are designed to align with mandates coming from the U.S. Environmental Protection Agency (EPA) and California Air Resources Board (CARB). In particular, PC-12 engine oils will support a 75% cut in nitrogen oxide (NOx) emissions and a 50% decrease in particulate matter (PM).
- Enhanced After-treatment System Performance: With modern engines relying heavily on diesel particulate filters (DPFs), diesel exhaust fluid (DEF), and selective catalytic reduction (SCR) systems, oils must now help preserve the performance of these technologies. PC-12 engine oils will support extending after-treatment service life from roughly 435,000 miles to 800,000 miles.
- Fuel Economy Improvements: Formulations will include lower-viscosity oils to reduce internal engine friction and boost miles per gallon.
- Futureproofing: PC-12 engine oils are engineered to support further technological advancements in diesel engine design, giving OEMs more room to innovate on high-efficiency powertrains.
The API’s official licensing date will be no later than Jan. 1, 2027, timed to coincide with the release of the next generation of compliant diesel engines.
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Understanding the Development of PC-12 Engine Oil Requirements
Now that you’ve gotten an overview of this new API diesel engine oil classification, it can be helpful to understand how these diesel engine standards evolved over time. The current heavy-duty oil classifications—API CK-4 and API FA-4—were licensed in 2016 as part of Proposed Category 11 (PC-11). These standards were developed to address increasing demands for engine protection and fuel efficiency in both legacy and emerging engine technologies:
- CK-4 Engine Oils: Designed for high durability and backward compatibility with older engines.
- FA-4 Engine Oils: Introduced lower-viscosity options, mainly for newer engines seeking improved fuel economy and thermal efficiency.
Since their release, the trucking industry has seen significant hardware evolution, with OEMs pushing the limits of performance, emissions reduction, and efficiency. FA-4 laid the groundwork for this, but industry needs have now outgrown PC-11’s capabilities. In response, API officially approved the development of PC-12 engine oils in early 2022. PC-12 builds upon PC-11 while incorporating new formulations to meet more stringent emission and durability requirements.
The Two Parts of PC-12 Engine Oil: PC-12a and PC-12b
To accommodate both legacy equipment and cutting-edge engines, PC-12 is being split into two distinct subcategories. Understanding the functional differences between these categories can help you select the right oil for your specific mix of trucks and operational needs.
PC-12a: Supporting Legacy Engines
PC-12a oils are fully backward compatible, meaning they are suitable for older engines already in service today. These formulations ensure that legacy equipment continues to receive reliable lubrication and wear protection, even as emission and efficiency demands increase.
For fleets running a combination of newer and older vehicles, PC-12a offers a consistent solution that maintains engine integrity while helping companies meet regulatory and sustainability goals.
PC-12b: Optimized for Advanced Engines
PC-12b is designed specifically for next-generation diesel engines. This subcategory will include lower-viscosity oils such as xW-20, which help reduce internal engine drag and enhance fuel economy—a critical consideration for long-haul operations where every gallon counts.
While PC-12b oils are not backward-compatible with older engines, they will be the go-to choice for fleets investing in the latest engine technologies and seeking to maximize fuel efficiency, extend oil drain intervals, and stay ahead of future emissions standards.
Exploring the Benefits of the PC-12 Engine Oil Standards
Beyond regulatory compliance, PC-12 engine oils bring a host of advantages to diesel fleets.
#1. Longer Engine Life and Reduced Wear
Optimized additive packages prevent engine wear under high-load conditions. This is crucial for protecting vital components in heavy-duty engines operating under greater pressure and heat.
#2. Better Resistance to Thermal Breakdown
Improved oxidation stability means oils won’t break down as quickly under high temperatures. This allows for extended oil drain intervals (ODIs) and fewer oil changes, ultimately minimizing your downtime and maintenance costs.
#3. Compatibility Across Engine Types
With PC-12a and PC-12b covering a wide spectrum of engine generations, fleet operators like you gain the flexibility to use the right oil for each application—from older high-mileage trucks to the latest emissions-compliant rigs.
#4. Enhanced Fuel Efficiency
Low-viscosity oils reduce resistance within the engine, improving fuel economy without compromising protection. This is especially beneficial for over-the-road trucks that clock hundreds of thousands of miles annually.
#5. Competitive Edge
Adopting PC-12 engine oils also helps fleets demonstrate environmental responsibility. This can enhance your brand’s reputation and appeal to customers, vendors, and stakeholders who prioritize sustainable business practices.
#6. Lower Operating Costs
Better fuel economy, longer ODIs, and improved engine durability all contribute to a lower total cost of ownership (TCO), a key performance metric for any fleet.
How to Ensure Compliance with New Emissions Regulations
PC-12 engine oils will be subjected to rigorous testing protocols to ensure they meet the demands of modern diesel engines and emissions hardware.
Two of the most notable tests include:
- Detroit DD13 Scuffing Test: This test evaluates an oil’s ability to prevent metal-to-metal contact under extreme conditions. Since modern engines run hotter and at higher pressures, scuff resistance is critical for avoiding engine wear and premature failures.
- Cummins ISB Viscosity Test: This test ensures that oils maintain the correct flow characteristics across various temperatures and engine speeds. Consistent viscosity is essential to maintaining effective lubrication from cold starts to high-load operations.
Other testing criteria focus on oxidation resistance, volatility, shear stability, and after-treatment compatibility. PC-12 engine oils must protect DPFs, SCR systems, and other components from ash buildup, fouling, and excessive deposits, all of which can compromise emissions compliance. By simulating real-world operating conditions, these tests verify that PC-12 engine oils will perform reliably across all types of fleet environments.
Get Ready for the Transition to PC-12 Engine Oils
Is your fleet prepared for PC-12 engine oils as 2027 approaches? We know a change in API diesel engine oil classifications can be overwhelming—especially as you evaluate your current inventory and plan for mixed equipment profiles. At Keller-Heartt, we’re your trusted partner in navigating the future of diesel lubrication. Our experts will keep you updated with the latest PC-12 news. Plus, we’re ready to supply you with high-quality PC-12 Shell products that meet demanding new standards. Have questions or want to learn more? Get in touch with us.
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