OEM views on PC-12

OEMs tell us what they are hoping to see in the new heavy-duty engine oil category

Driven by big changes to North American emissions regulations scheduled for 2027 and beyond, Truck and Engine Manufacturers Association (EMA) members have asked the American Petroleum Institute (API) for a new heavy-duty diesel engine oil category ready for MY 2027 vehicles. Insight talks to a number of industry stakeholders about the changes they expect to see in the new PC-12 category.

There's no doubt that current API CK-4 and FA-4 oils have been doing a good job. However, tightening emissions legislation coming in 2027 means EMA has requested the new heavy-duty engine oil category to ensure engine and aftertreatment systems are sufficiently protected over extended warranty and useful aftertreatment life periods.

To meet the proposed oxides of nitrogen (NOx) limits OEMs will need to make significant aftertreatment system changes. Whilst a number of configurations of the various aftertreatment systems are being explored, close-coupled selective catalytic reduction (SCR) technology, in combination with diesel oxidation catalysts, catalysed filters and secondary SCR look set to be the technology of choice for future low NOx heavy-duty on-road diesel engines. The protection of the close-coupled SCR is a key factor, and it will be important to balance the protection of these systems with other lubrication requirements.

Tightening chemical limits

One of the key changes that has been proposed by OEMs for PC-12 oils is a tightening of the chemical limits to help protect the latest aftertreatment equipment and emissions devices. This is seen as vital with the extension in the useful life of aftertreatment devices to 650,000 miles and engine and aftertreatment warranties to 450,000 miles in 2027. Wei Qin, a material science engineering specialist at Cummins and Suzanne Neal, Powertrain Fluids Engineer from Daimler Truck North America share their thoughts.

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Wei Qin, Cummins and Suzanne Neal, Daimler Truck North America

The need for longer aftertreatment useful life will create more stringent requirements for oil formulations as some chemicals in engine oils, for example, sulphur, phosphorus and sulphated ash are known to have adverse effects on aftertreatment systems. Our internal study has shown the negative impact caused by those chemicals on aftertreatment components. Reducing the content of those chemicals, while meeting other performance requirements, is critical in meeting those extended aftertreatment useful life goals.


To address this within PC-12, the chemical limits have been lowered for components such as phosphorus and sulphur to protect the future aftertreatment designs. In addition, sulphated ash will be lowered to help extend maintenance intervals.

For model year 2027, Detroit will introduce new engine oil specifications aligned with the launch of PC-12.  To address the increase in full useful life and aftertreatments, Detroit specifications will include limits for potassium and sodium in addition to the PC -12 chemical limit reductions in phosphorus and sulphur. For the increase in full useful life for engines, Detroit specifications will include internal wear tests in addition to the PC-12 wear tests

Setting lower chemical limits for an oil restricts the formulation space and removes components that have specific jobs to do, such as wear protection and detergency. There needs to be a careful balance to ensure lubricants continue to deliver sufficient component durability and extended aftertreatment protection.

Extending drain intervals

Vehicle durability and reliability along with lower running costs are key differentiation criteria for fleet owners. Suzanne Neal and Ryan Denton, Corporate Chemical Technology Manager at Cummins talk about the need to offer extended equipment life and operational reliability over longer oil drain intervals.

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Suzanne Neal, Daimler Truck North America and Ryan Denton, Cummins

Oil drain intervals have evolved throughout the years. In today's modern engines, oxidation is the main driver for oil drain intervals rather than TBN. In 2017, Detroit decided to provide longer drain interval options for our customers. Many of our major fleets have taken advantage of these longer intervals because it helps reduce the amount of oil used during the lifetime of the truck and reduces the total cost of ownership for fleets.

An engine oil performance need that is of particular interest to Detroit is oxidation. The limits for oxidation will be tightened in the new PC-12 category. This is important because oxidation is one of the limiting factors for oil drain intervals in modern engines.


In the last five to ten years, the quality of modern oils and improved Cummins engine designs have allowed extended oil drains in service literature across many engine platforms. In addition, Cummins recognised a greater potential for customer specific oil drain extensions based on their unique duty cycle and maintenance programme. We're currently using large data sets from that programme to help pursue new opportunities in the digital space for even greater optimisation.

Even lower viscosity

OEMs are working to achieve fuel economy improvements, motivated both by customer demands for lower running costs and by tightening greenhouse gas (GHG) emissions regulations. The use of lower viscosity engine oils is one of the key levers in reducing fuel usage and PC-12 is expected to enable the introduction oils with lower viscosity than those available in API FA-4 today. Wei Qin and Suzanne Neal give their views on the transition to lower viscosities.

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Wei Qin, Cummins and Suzanne Neal, Daimler Truck North America

As greenhouse gas limits become tighter, we expect to see further usage of API FA-4 viscosity fluids. We're validating FA-4 viscosity fluids in many of our highway engine programmes in the years ahead.

Currently we're seeing wider adoption of API FA-4 oils in our engines, but the need to go to lower viscosity oils is not clear.


From our discussions with fleets, the two main topics that come up are longer drain intervals and fuel economy. Longer drain intervals can help fleets achieve reduced downtime and less oil changes to help meet their sustainability goals. As fleets transition to lower viscosity oils such as SAE 10W-30 API FA-4, this will help the fleet improve their overall fuel economy.

The next diesel engine oil category, PC-12, will include an additional viscosity grade SAE XW-20, which is not currently available in API FA-4.

The wider use of low viscosity lubricants in heavy-duty applications means maintaining engine durability is more essential than ever before.

Education on PC-12

The momentum is building towards the introduction of the new heavy-duty engine oil category in 2027. As API’s Jeffrey Harmening and Suzanne Neal explain there will be a real need to educate diesel engine oil consumers about the changes that have been made and benefits of switching to the latest oils.

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Suzanne Neal, Daimler Truck North America and Jeffrey Harmening, API

One of the biggest challenges to come is how to educate and prepare the market for the introduction of PC-12. As we learned in PC-11, it is important to start education to the market as soon as possible. From our discussions with fleets, they are excited to learn more about PC-12 and want to help in any way they can to avoid market confusion. 


The challenges remain the same; properly educating the diesel engine oil consumer and the oil changing public. As the NCDT [new category development team] wrestles with the long list of needs that it's addressing, it's clear that added complexity and possibly even separation of on-highway and off-highway needs is forthcoming. It'll be more important than ever to all of us to ensure that these future oils are properly applied and we all have a major role to play in that charge.

There is still much to do to get PC-12 across the line to meet EMA timings of a first allowable use on January 1 2027. Sign up here to receive our latest articles to keep up to date with the changes.


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