PC-12 stands for Proposed Category 12. It is the development name for the next generation of heavy duty diesel engine oil standards being introduced for 2027.

The new standards are designed around changing engine technology, tighter emissions requirements, longer useful-life expectations and opportunities to improve efficiency while maintaining engine durability.

First licensing for the new API categories developed through PC-12 begins January 1, 2027.

That date marks the beginning of the new categories. It does not mean every fleet needs to change lubricants or maintenance practices on January 1.

A major driver is the next generation of emissions requirements for model year 2027 heavy duty engines.

The requirements call for sharply lower nitrogen oxide and particulate matter emissions while also extending how long engines and emissions-control systems must meet emissions standards. Engine manufacturers are developing new technologies to meet those requirements and engine oils must evolve with them.

CL-4 and FB-4 are the two new API service categories being developed through PC-12.

CL-4 succeeds CK-4. FB-4 succeeds FA-4.

They address different equipment and viscosity needs, so understanding which category is appropriate will be important during the transition.

CL-4 is designed for broad application and backward compatibility with engines that currently call for CK-4 oils.

FB-4 supports lower-viscosity oils for engines designed and approved to use them. OEM recommendations will be especially important when determining whether FB-4 is appropriate for specific equipment.

Backward compatibility means a newer oil category is designed to meet the needs of equipment that calls for the category it replaces.

For PC-12, CL-4 is designed to be backward compatible with CK-4 applications. Fleets should still follow OEM recommendations for their specific equipment.

Lower-viscosity oils can reduce internal friction and pumping losses, creating opportunities to improve fuel efficiency.

PC-12 is designed to support those lower viscosities while still requiring the oil to meet defined standards for wear protection, oxidation control and other critical performance areas.

No. Viscosity is only one characteristic of engine oil. Oils carrying the new categories must meet defined performance requirements. The more important question is whether the oil meets the required standard and is appropriate for the engine based on OEM guidance.

No. January 1 marks the beginning of first licensing for CL-4 and FB-4. It is not a deadline requiring every fleet to change lubricants immediately.

Equipment age, application, OEM recommendations, current lubricant requirements and fleet replacement cycles will influence when or whether changes make sense.

No. An on-highway fleet adding 2027 equipment may encounter CL-4 or FB-4 sooner than an off-highway operation running older equipment. Mixed fleets may also have several generations of engines and lubricant requirements operating at the same time.

The right transition plan will depend on the equipment being protected.

Mixed fleets may need to manage more than one oil category or viscosity during the transition.

Understanding which engines can use CL-4, which equipment may eventually be approved for FB-4 and where existing oils remain appropriate can help prevent compatibility issues and unnecessary complexity.

Do not assume so. There is currently no announced API sunset for CK-4. Existing and new categories may coexist as fleets, OEMs, distributors and lubricant suppliers move through the transition at different rates.

Possibly. Fleets using multiple categories, viscosities or equipment generations may need to review bulk storage, labeling, inventory practices and technician guidance to reduce the risk of using the wrong oil in the wrong application.

The need for those changes will depend on the fleet.

Not automatically. A new API category does not by itself extend drain intervals. OEM guidance, operating conditions, oil analysis and other validation should continue to drive drain-interval decisions.

Some lower-viscosity oils introduced within the categories may create opportunities for improved fuel efficiency by reducing internal friction and pumping losses.

Actual results will depend on the oil, equipment, application and operating conditions.

Engine oil formulation can affect emissions-control components such as diesel particulate filters.

CL-4 tightens limits on certain chemical components that can contribute to ash accumulation, helping support the performance and useful life of these systems while maintaining engine protection.

Don’t assume different oils can be mixed as part of the transition.

Compatibility can depend on the oil categories, viscosity grades, equipment requirements and OEM guidance involved. Fleets should confirm the appropriate approach with their lubricant supplier and engine manufacturer before combining products or changing service-fill practices.

Warranty requirements are established by individual OEMs.

Using the correct oil category and viscosity for the engine remains important, so fleets should follow the manufacturer’s service recommendations as guidance becomes available.

Pricing will depend on the product, formulation, viscosity grade and market conditions.

For fleets, purchase price is only one consideration. Lubricant selection should also account for equipment protection, fuel efficiency opportunities, maintenance requirements and overall operating cost.

Phillips 66^® Lubricants will continue tracking developments as OEM guidance, product information and transition recommendations become available.

The goal is to help fleets understand what matters now, what can wait and what questions to ask as the market moves toward 2027.