Years of work are under way to develop two new diesel-engine oil service categories to help hit...

Years of work are under way to develop two new diesel-engine oil service categories to help hit emission targets and boost engine performance.


It’s time to bake the donuts, again. The American Petroleum Institute’s Lubricants Group has established a New Category Development Team to launch the test-development phase of what will become a fresh pair of API diesel engine oil service categories.

While under development, the process will be known as PC-12. Over the next five or so years, motor oil formulators, engine builders, and additive suppliers will work together toward the release of two new specs for formulating oil engineered for heavy-duty diesel engines.

Once approved for licensing, each of the new categories will get its own API service-symbol “donut.” Those new oil specs, slated to roll out in 2027, will go beyond the performance standards set by the last two diesel service categories announced by API in 2016, FA-4 and CK-4.

The Engine Manufacturers Association requested development of new category specs to help meet the demands of upcoming greenhouse gas/fuel mileage regulations, says Jeffrey Harmening, manager of the Engine Oil Licensing Certification System for API.

The request for first-licensing date from API is no later than January 1, 2027, which coincides with the anticipated 2027 implementation date for EPA and CARB heavy-duty on-highway regulations, he explains. “This is similar to the PC-11 [the previous test category] licensing timeline that resulted in API CK-4 and FA-4,” he says.

By this December, EPA has said it will finalize new stringent emissions standards to reduce nitrogen oxides (NOx) pollution from trucks starting in model year 2027. This will include an update of current GHG standards. The agency is also working on even tighter GHG standards for heavy-duty engines and vehicles starting as soon as model year 2030.

As with the twin categories birthed by PC-11— CK-4 and FA-4 — PC-12 will a produce a “‘C” subcategory (to replace CK-4) that will maintain its backwards compatibility (engineer-speak for a formulation approved for all) and a new “F” subcategory (to replace FA-4) that won’t require backwards compatibility.

Harmening says development of the next “F” subcategory will look at further reductions in viscosity to help engine builders meet tighter fuel economy targets. But “C” oil retaining backwards compatibility doesn’t mean little will change. Rather, he says that developing a new “C” will consider oil performance in engines using newer technology, such as elastomer seals, and whether the T-11 and T-12 engine-wear tests used during recent category developments should be replaced.

The Split

“The big highlight of the 2016 [API rollout] was the split between the ‘C’ and ’F’ categories,” says Karin Haumann, Shell Lubricants’ OEM technical manager, who serves as chair of the New Category Development Team for PC-12.

“Backwards compatibility is always a factor,” she points out, but in 2016, “the categories had to diverge due to engine hardware changes being made to accommodate new technology” to meet stiffening emission standards.

“Proposed U.S. EPA and CARB standards aim to limit tailpipe emissions of nitrogen oxides while also requiring improved vehicle efficiency,” says Shawn Whitacre, senior staff engineer for Chevron Lubricants. “These new standards, if promulgated, would also put greater emphasis on the ‘useful life’ of the emissions control system.”

Whitacre says that at a high level, “EMA has requested further improvements in oxidation stability and wear protection while also seeking to leverage lower-viscosity grades to unlock additional fuel efficiency.”

The current specification requirements include nine fired engine tests and several other bench tests, and some need to be replaced.

“Some of the engine tests were developed more than 20 years ago and rely on test hardware that is no longer in production,” Whitacre says. “It is also recognized that some of these legacy tests have more limited relevance to more modern hardware.”

Many of these engine tests are targeted at gauging the oil’s ability to handle high levels of soot. “This was critical to protect older engines, but advancements in combustion, emissions control, and hardware make it less of a concern today,” he explains.

Shell’s Haumann also says engine makers want to see PC-12 result in better oxidation performance of the oil. She said two new engine wear tests are now available to help update PC-12 criteria as well.

The Lubricant Limbo

Continued focus on lower-viscosity formulations will be a hallmark of the next “F” oils.

“You’ll hear ‘as low as XW-20, which may indicate going down to 5W-20 or 0W-20,” Shell’s Haumann says. “The lowest is not in the forecast here in the U.S., but the process is long, and that means keeping a category active for 10 years.

“In other words, a category can take in futureproofing by setting up the ability for test limits for further performance requirements as sought by engine makers,” she explains. “That’s a unique attribute of PC-12.”

Chevron’s Whitacre expects the next F category will likely encompass lower-viscosity SAE 5W-30s and 10W-30s, as well as XW-20s.

“As is the case today, not all engine builders will recommend these lower-viscosity grades,” he says.

He says engine builders want to prevent thermal breakdown of engine oils to enable extending oil drain intervals. “We made a big jump in oxidation stability with CK-4/FA-4, and they are asking for even more from PC-12 oils. This is clearly aligned with extended oil drain considerations.”

Drawing Board

A concern close at hand is what to do about the aforementioned engine tests. Along with deciding on whether to use the older T-11 and T-12 tests, Shell’s Haumann says the “DD-13 is a scuffing test used during PC-11 development but not adopted. Since then, the test has been more refined and is used within the Detroit Diesel oil spec. So, we’re considering it as an option within PC-12.

“The new category team will determine DD-13’s suitability for PC-12 within the next six to 12 months,” she continues. “As a scuffing test, it evaluates wear between the ring and the liner.”

Under consideration also for PC-12 is the Ford 6.7L valvetrain wear test. “This one is based on work Ford’s done on its hardware to ensure new oils perform adequately in the valvetrain,” she says. The 6.7L diesel is available on Ford’s medium-duty Super Duty trucks.

She offers a caution on the goalposts for the upcoming round of emission standards for trucks. “EPA is still determining what their GHG and NOx limits will be in 2027,” she says. “And once the engine builders know what those will be, they will have to determine what hardware changes they will need to make. Then, through PC-12’s development, the oil industry will work with them to meet the new limits.

“We do have an idea of what those standards will be, so the new category team is geared up for when the ballpark becomes clear,” she adds. “There’s a lot of work to be done, such as replacing some engine tests. We’re getting started with the items we know we must look at.”

The Lowdown on Low Viscosity

A low-viscosity motor oil is formulated to be less viscous so that it flows more smoothly at both hot and cold engine temperatures. Read the API donut assigned to an oil to determine its viscosity. With a 5W-30 oil, “5” refers to its viscosity characteristics at low temperatures and “30” at high temperatures.

Running a multigrade low-viscosity oil helps reduce parasitic losses in the engine, which boosts fuel efficiency. It also cuts warm-up time in cold weather, protecting the engine when it’s at increased risk of wear.

The HTHS (High Temperature High Shear) value, which became a factor in the last round of oil standards, “signifies the oil’s viscosity in the bearings and highly loaded parts at operating temperature,” points out guidance from Petro-Canada Lubricants.

The company lists other factors to weigh, including:

  • Industry-standard test results, such as for “Cold Crank Viscosity,” ensure critical components get optimal lubrication.
  • Results of specific tests by engine makers indicate that an oil surpasses the OE’s standards for engine protection and may afford approval of extended drains.
  • Low-viscosity oil demonstrating low iron wear levels will offer superior engine protection properties.
  • Fuel economy can be assessed in the field via tests such as the SAE J1321 Type II consumption test.

Engine oil specs should align with OEM recommendations, advises Petro-Canada. “This is crucial for maintaining a vehicle’s warranty and performance when it comes to both protection and fuel economy.”

This article first appeared in the May 2022 issue of Heavy Duty Trucking.

About the author
David Cullen

David Cullen

[Former] Business/Washington Contributing Editor

David Cullen comments on the positive and negative factors impacting trucking – from the latest government regulations and policy initiatives coming out of Washington DC to the array of business and societal pressures that also determine what truck-fleet managers must do to ensure their operations keep on driving ahead.

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