Change is coming for heavy-duty engine oils. The American Petroleum Institute’s Proposed Category 12 (PC-12) is currently under development. PC-12 will raise the bar for engine oil performance across a range of key criteria, including fuel economy, wear protection, and more. 

That means change is coming for the lubricants that heavy-duty trucking professionals use. The new PC-12 category for heavy-duty engine oils is scheduled to go into effect in January 2027, replacing the current API CK-4 category. It’s worth staying educated on what those changes mean.

Protecting Aftertreatment Devices

One of PC-12’s most noteworthy changes is enhanced protection for aftertreatment devices, including diesel particulate filters (DPFs) and selective catalytic reduction (SCR) systems. This will help to reduce the frequency of time-consuming regenerations and extend the life of DPFs. 

But how next-generation oils will accomplish this goal — a reduction in phosphorus and ash-containing anti-wear chemistry — has raised some questions about engine protection. It’s a formulation requirement that the lubricants industry is working diligently to satisfy.

In this article, we’ll explore next-generation lubricants and aftertreatment device performance, additional PC-12 updates, and their anticipated benefits for on-road vehicles, plus how trucking professionals can prepare and make the best lubricant choices for their operations.

Why Do We Need a New Oil Category? 

To understand some of the changes coming for next-generation lubricants, it can be helpful to understand the drivers behind them. 

Stringent new emissions standards are coming for on-road as well as for off-highway heavy-duty engines. 

Set by the U.S. Environmental Protection Agency in 2022 and coming into effect for model year 2027 engines, tomorrow’s trucks must achieve: 

• A 75% reduction in nitrogen oxide (NOx) emissions from current allowable levels.

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

• Extended service life for exhaust aftertreatment devices, growing from about 435,000 miles to 800,000 miles.

Meeting these new standards will be a significant challenge for original equipment manufacturers, requiring changes to hardware design and operation. 

Doubling the service life of aftertreatment devices is not simple. It will also require meaningful contributions from engine oils, which is why it's one of the main driving forces behind PC-12. 

Protecting Critical Aftertreatment Devices

One way to protect aftertreatment devices (SCRs and DPFs) and extend their service life has already been determined for PC-12: reduce phosphorus and ash-containing chemistry levels in heavy-duty engine oil. 

Highly efficient exhaust gas aftertreatment equipment allows trucks to meet EPA and California emission criteria. 

The selective catalytic reduction (SCR) system reduces NOx levels in exhaust gases through the action of a metal catalyst in conjunction with diesel exhaust fluid to produce benign byproducts. 

However, during engine operation, phosphorus in the lubricant can enter the exhaust and react with the SCR’s catalyst, reducing its activity. This leads to a drop in the effectiveness of the system to reduce emissions and shortens the lifespan of aftertreatment devices. 

Therefore, low-phosphorus formulations are required to prolong the functionality of the aftertreatment device. As a result, phosphorus levels in PC-12 fluids will be limited to 800 parts per million (ppm), a 30% reduction from the 1200 ppm figure allowable in current oils.

But phosphorus has historically been used in engine oils for an important reason: providing reliable wear protection. 

Specifically, zinc dialkyldithiophosphates (ZDDPs) have been widely used for anti-wear properties for many years. ZDDPs also help to inhibit oxidation and deposit formation within the lubricant formulation. Historically, they’ve been an important tool in the oil formulator’s toolbox.

Formulators have been developing alternative formulations with new chemistries that can stand up to the demands of heavy-duty equipment. 

Various phosphorus-free anti-wear chemistries have shown that effectiveness across each performance area will require more than a simple one-to-one replacement. A combination of several additive chemistries will be needed to replace ZDDPs.

However, heavy-duty trucking professionals can rest assured that effective formulations will be available despite the new formulation restrictions. Low-phosphorus formulations are already available today and are commonplace in global markets. 

The Benefits of Low-Phosphorus, Low-Ash Oil Formulations

Enhanced aftertreatment device protection in next-generation engine oils can have a real impact on heavy-duty trucking fleet operators.

Consider that DPF regeneration (often simply referred to as “regen”) is an essential maintenance procedure for fleets. This process, which burns off soot and particulates that accumulate in the DPF, is critical for keeping emissions systems working properly and maintaining expected engine performance. 

Passive regeneration happens automatically during normal on-road activity when exhaust temperature reaches appropriate levels, but fleets must often perform active or manual regeneration for excessive buildup:

• Active regen requires the engine to inject extra fuel into the exhaust stream to reach the right temperatures. It may occur while driving or idling. 

• Manual regeneration must be performed while the truck is parked and may take anywhere from 30 to 60 minutes. 

Both processes require extra resources, such as extra fuel, downtime, or both, which can add up across an entire trucking fleet. 

Next-generation lubricants will better contribute to the health and longevity of engine’s aftertreatment equipment, reducing downtime and maintenance.

On top of that, lubricants that can contribute to extended lifespans for DPFs can save fleets on repair or replacement costs. 

These savings, taken across an entire fleet, have the potential to add up to a significant benefit for the bottom line.

Additional Benefits for Higher-Performing Engine Oils

Lubricants that meet the elevated standards of PC-12 can also contribute to enhanced fuel economy. 

Like API CK-4 and its lower-viscosity counterpart FA-4, PC-12 will be split into two categories. 

The F category will be intended for new-model trucks and will contribute to improved fuel economy. For trucking fleets, it’s worth investigating these lower viscosity formulations. Compared to traditional 15W-40 grade lubricants, trucks can see a 1-2.2% improvement in fuel economy by choosing a low-viscosity FA-4 oil. 

While it may sound like a small gain per truck, it can add up to significant savings across an entire large fleet. Start by ensuring OEM approval and work with your oil supplier to evaluate your options.

OEMs, oil marketers, and additives suppliers continue to work closely to ensure that end users can depend on reliable, effective solutions that allow heavy-duty equipment of all types to perform as intended. 

While 2027 may seem far off, fleets can start preparing themselves for next-generation fluids today. It is worth consulting with your lubricants suppliers early and often about PC-12-compliant fluids. Engagement in early-stage collaboration, testing, and on-road use can best prepare your fleet for success when PC-12 sees first license, and is critical for developing reliable new fluids. The entire heavy-duty trucking industry stands to benefit.

About the author: Zachary L. Rodgersis the Engine Oil Development Manager at Lubrizol Additives, where he leads formulation strategies for heavy-duty engine oils. He specializes in North American heavy-duty and Latin American passenger car product development. 

This article was authored and edited according to Heavy Duty Trucking’s editorial standards and style to provide useful information to our readers. Opinions expressed may not reflect those of HDT.