As you read this, industry stakeholders are hard at work developing the American Petroleum Institute’s (API’s) Proposed Category 12 (PC-12), the next performance category for heavy-duty diesel engine oils. Industry bodies, original equipment manufacturers (OEMs), oil marketers, and others are working toward a January 2027 first-license date for PC-12 to align with major shifts in emissions requirements for new-model equipment. 

For heavy-duty trucking fleets and other operators of commercial diesel equipment, this means that the engine oils you use to service your vehicles regularly will soon deliver higher levels of performance across a broad range of performance requirements, including:

• Enhanced engine protection

• Greater compatibility with diesel particulate filters

• Better fuel economy

And more. Importantly, PC-12 will be split into two subcategories, most likely to be named API CL-4 and API FB-4. The latter will further classify lower-viscosity formulations designed specifically to enhance fuel economy, delivering new value across the heavy-duty diesel landscape and significant potential savings for fleets. Here’s what trucking professionals need to know: 

Understanding PC-12: The Next-Gen Diesel Engine Oil Standard

First, it’s helpful to understand the drivers behind PC-12’s development. In 2022, the U.S. Environmental Protection Agency (EPA) released stringent new emission standards, which will take effect for model-year 2027 diesel engines and include: 

• A 75% reduction in nitrous oxide (NOx) emissions.

• A 50% reduction in particulate matter (PM). 

• Extended service life requirements for aftertreatment systems, from about 435,000 miles to 800,000 miles. 

To meet these requirements, heavy-duty diesel OEMs have been busy overhauling engine and drivetrain hardware, especially aftertreatment devices. Simultaneously, they issued a request for a new engine oil performance category to help them meet such limits—thus the development of the PC-12.

Beyond simply enabling emissions requirements, PC-12 developers are also aiming to deliver new value to end users through enhanced engine protection, longer oil drain intervals, and improved fuel economy.

How the New F Category Oils Could Boost Fleet Fuel Economy

As noted earlier, category developers will again introduce a new “F” category, which currently classifies lower-viscosity lubricants that can contribute to improved fuel economy. 

The current low-viscosity category, FA-4, has not seen significant adoption by fleets and other end users. However, there is an expectation that the next category will see greater uptake.

Why? First, major OEMs have signaled greater willingness to approve the use of F-category lubricants in their new-model vehicles in 2027 and beyond. Second, the lack of OEM approvals for FA-4 lubricants was a significant reason why demand has remained low, but this may be changing for the next API category.

Servicing your vehicles with OEM-approved fluids and lubricants is essential for staying within warranty. But it is also important to remember that the new F category will represent the best that the heavy-duty diesel engine oil market has to offer. 

F category lubricants and their next-generation counterparts must necessarily meet the same performance rigor as their C category counterparts under PC-12. This means OEMs and end users alike can be confident in excellent levels of wear protection, as well as the fuel economy benefits F category fluids can deliver.

And the benefits of choosing lower-viscosity oils are significant. Fleets can realistically expect fuel savings of 0.5%-1.5% by switching from 15W-40 to 5W/10W-30 engine oil. The savings from switching to fuel-efficient F variants are expected to add an additional 0.4%-0.7% in fuel efficiency. Throughout a lifetime of service, F category fluids can deliver significant operational cost savings. 

Lower-viscosity fluids are also highly complementary to current trends in engine design. Modern engine hardware works very hard to deliver greater efficiency, and a thinner lubricant inherently reduces some engine stress by allowing it to move with less resistance. 

Over the course of an engine’s life, that kind of stress can add up, and it means that lower viscosities can contribute to a longer useful life for an engine, all while delivering efficiency benefits. For any fleet, longer-lasting vehicles can make a big difference for the bottom line. 

Do Lower-Viscosity Oils Protect as Well? Here’s the Proof

One source of hesitation in adopting and specifying lower-viscosity F category fluids has stemmed from an outdated perception of engine oil technology, that “thicker” is always better for wear protection.

Understandably, fleet operators want assurance that the lubricant will provide long-term engine protection. Equipment OEMs want the same. And low-viscosity fluids have now demonstrated reliable performance for many years across both new- and older-model engines in a broad range of applications. 

To that end, Lubrizol has field-tested FA-4 lubricants in real-world engines from a variety of OEMs, accumulating over 86 million miles of testing. Findings were clear: Engines, old and new, are showing expected levels of wear up to 500,000 miles of service while achieving significant fuel-economy improvements. The fact is that viscosity is not a key indicator of protection. Proper formulation with the right additive technology is.

How Fleets Can Prepare for the Next Generation of Engine Oils

The widespread adoption of new technologies will be increasingly necessary as global initiatives to reduce emissions continue apace. F category lubricants represent one of those technologies, contributing to greater fuel economy while protecting new heavy-duty trucks for extended service lives.

For fleets, the benefits are clear. Adopting lower-viscosity fluids can lead to significant cost optimization through fleet-wide fuel-economy gains. It is worth opening the conversation with your lubricant suppliers to vet the options available.

Lubrizol's testing and development efforts show that wider use of advanced F-category lubricants can provide measurable benefits for both OEMs and fleet operators. These next-generation fluids support engine hardware in performing efficiently while helping fleets improve fuel economy. As emissions standards evolve and operating costs rise, the role of high-performance lubricants will only become more essential for heavy-duty applications.