New EPA 2027 emissions rules also mean new diesel engine oil specs. A new generation of heavy-duty engine oils will feature lower viscosity, improved thermal resistance, and possibly longer oil drain intervals.

In conjunction with an event showing off its Starship technology demonstrator truck, Shell recently offered an update on the current state of the heavy-duty diesel engine oil category being developed by the American Petroleum Institute to meet the needs of the new generation of engines.

The current oil category is actually two — CK-4 and FA-4 categories, depending on viscosity requirements. Launched in 2016, those categories were the first time the heavy-duty diesel engine category had been split in two.

However, new diesel engine emissions regulations from the Environmental Protection Agency further limiting NOx (Nitrogen Oxides) emissions come into effect on January 1, 2027. Those regulations require hardware changes on equipment. And those, in turn, require some additional performance characteristics from the oil that lubricates those engines.

Lower-Viscosity Oils

API spent about a year evaluating the current category to determine if an upgrade was feasible. Once that was decided, API then had to define what the new requirements would be, explained Karin Haumann, Shell OEM technical manager for heavy-duty engines.

The end result, she said, will be a move toward lower-viscosity oils for heavy-duty diesel engines with a new "FB" category, which will include the addition of 5W-20 and 0W-20 grade oils.

“European truck OEMs use lower viscosity grades,” she noted. “And we expect this new category to remain the industry standard until 2040.”

The new oils will offer fleets numerous improvements, including better oxidation stability, which means better thermal resistance for the oil.

“That will allow the OEMs to potentially extend oil drain intervals,” she added.

“When you have better oxidative stability, that allows the OEMs to do one of two things: Either run the engine hotter to be able to manage viscosity and efficiency that way or extend oil drain intervals.”

OEMs could opt to do both, Haumann said, although she noted that would be something of a balancing act.

“I do think the trend will be going toward extending current drain intervals,” she said. “But that will probably happen on a case-by-case basis for each engine OEM.”

Tough New Aftertreatment Regulations

The biggest issue facing the new oil category will be the much longer lifespan and performance required of 2027 diesel exhaust aftertreatment systems.

“The [Truck and] Engine Manufacturers Association came to API and asked if we could help them with the new aftertreatment systems,” Haumann said.

That's because the new regulations also extend the definition of "useful life" of both the engine and the aftertreatment system.

The EPA will expect a new truck’s exhaust aftertreatment system to last and maintain near-peak efficiency (or close to it) throughout the life of the truck. The current “useful life” of a diesel engine is defined by EPA as 400,000 miles. For 2027 model trucks, that useful life number will increase to 650,000 miles.

“EPA is also requiring longer warranties for exhaust aftertreatment systems,” Haumann said.

“That’s to discourage any disabling of or workarounds to defeat the systems. Or help fleets avoid having a relatively new truck on its hands that is polluting. They’re shifting that responsibility onto the OEMs, so the customers don’t have to worry about it.”

Will New Oils Be Backward-Compatible With Current Ones?

API is working hard to ensure the new oil category will be backward compatible with current diesel engine lubricants as well, Haumann said.

The first step in that process will be to retire some older engine oil tests and establish new ones.

“We have several engine tests that are required for the API categories that are going away,” she explained, “because the parts needed to run them are becoming depleted. 

"In order to maintain backward compatibility, we have to have some kind of substitute or some kind of assurance that the new category without that test is still going to have the same performance as the older category.”

Three PC12 tests will be carried over. A new test, dubbed the DD13 Scuffing Test, along with a replacement test for the existing T-11 Soot Handling test, will replace three older ones being retired.

The industry does not have enough engine hardware to support three of the current tests through 2040, Haumann said. However, the performance of those tests is redundant to existing tests. So if an oil fails one of the new tests, it will also fail the tests that aren’t being carried over.

“That gives us assurance that we’ve established good backward compatibility with the CK oils,” she said.

Backward compatibility in the FA-4 portion of the category is a little different, though. That’s because lower-viscosity oils are intended for new-technology engines that generate lower levels of soot than older engines do.

That, in turn, means the new oil category, presumably to be called FB-4, will not need the same soot-handling requirements as FA-4 blends do.

“We’ve lowered the soot-handling requirements for the new category,” Haumann said. “But other than that, all of the performance requirements are equal to or better than CK-4 and FA-4. So, they will be backward compatible.”

The first licensing date for the new API heavy-duty engine categories will be January 1, 2027. That date corresponds with the new EPA NOx regulations that go into law on that day, as well.

“The OEMs are going to require these new oils be used on 2027 model year engines and newer,” Haumann says. “You can expect the new oils rolling out early January 2027.”