PC-12 could face backwards compatibility issues

In early March, the American Petroleum Institute (API) received a request for a new heavy-duty engine oil category from the Truck and Engine Manufacturers Association (EMA). Since the request, API’s New Category Evaluation Team (NCET) has been evaluating the application to determine if a new category is merited. “PC-12” will supersede the most recent API service category for heavy-duty engine oils, API CK-4 and FA-4, that were launched in 2016.

EMA has provided greater clarity on PC-12 engine oil performance. During an NCET meeting on October 5, EMA outlined high-level requirements — which incorporated findings from the NCET subgroup reports and recent EMA surveys. While the presentation provided a clearer sense of what EMA is asking for, the overarching theme of the meeting was of uncertainty — that is likely to create challenges in the development of the new category. 

PC-12 is intended to align with ambitious future goals for fuel economy and emissions, and forthcoming engine technology arising from new U.S. regulations which have not been decided yet. EMA underlined the vagueness around future regulations that remain outside of their control, such as the finalisation of the California Air Resources Board (CARB) and the U.S. Environmental Protection Agency (EPA) regulations.

On August 5, 2021, the EPA announced it was working on a series of major rulemakings over the next three years that would reduce greenhouse gas (GHG) emissions and other harmful air pollutants from heavy-duty trucks. The rulemaking will be finalised in 2022, according to the EPA, and will apply to heavy-duty vehicles from model year (MY) 2027 — a similar timeframe to the launch of PC-12. The announcement also signposted additional, more robust, GHG emission standards as early as MY 2030 and beyond. Heavy-duty regulation accompanies plans for tighter federal GHG emissions standards for passenger cars and light trucks.

CARB’s proposed regulation for medium- and heavy-duty zero-emission fleets is designed to mandate wide-scale and rapid adoption of battery-electric and fuel cell-powered trucks in the state of California, which historically has adopted regulations that are even more stringent than the U.S. federal agency. The rule has not yet been approved but has been sent to the CARB Board for a decision in December 2021.

Concerns remain around future changes to EPA regulations

In general, EMA knows where these regulations are heading, and considerations were used to develop the needs for PC-12. However, concerns remain around future changes to EPA regulations and the impact these could have on new category development. EMA will provide further updates as the information becomes available. Though, with EPA targeting December 2022 for the release of the new standards, there is very little wiggle room for the planned implementation of PC-12 in 2027. Ash is currently the biggest issue on the table concerning this legislation.

The EMA presentation outlined the specific areas of focus for OEMs in the development of the new category. PC-12 may be divided into on- and off-highway, with high temperature, high shear (HTHS) the major differentiator. An on-highway standard may maintain two distinct subcategories, C and F, preserving the current F category HTHS limits. There is OEM interest in considering lower viscosity, lower HTHS limits than the current 2.9 minimum, due to a potential need for this oil. EMA also recommended consideration of subgroup two’s survey regarding the expansion of the F category to include additional SAE viscosity grades. Off-highway will continue with the C category as defined in PC-11 HTHS limits, which is a minimum of 3.5 cSt.

OEMs are asking for improved oxidation in PC-12, with the possibility of tighter limits. Improved wear protection was also highlighted by EMA.

EMA is no longer requesting changes to existing test soot limits for PC-12. Backwards compatibility requirements for the C categories, engine test availability, and results from the NCET subgroup, were cited as reasons for the revision. Though, future engine technology may require lower/optimised soot limits compared to current levels.

Elastomers have not been reviewed in any depth for several years. EMA provided three recommendations including improving the current elastomer test by adding materials provided from the EMA survey; aligning with ACEA E9, CEC L-11-16 test where possible, and consideration of other industry elastomer activities — such as the potential to include SAE J2979, a test method for vulcanized rubber and thermoplastic elastomer determination of compressive stress relaxation response, as an additional requirement.

Europe has required low SAPs (Sulphated Ash, Phosphorous, and Sulphur) oils for some time. Aftertreatment life is directly linked to lower SAPs. EMA outlined its commitment to maintaining compatibility with modern aftertreatment systems. However, concerns were raised around differences between parameters in the European and American specifications that could create issues with backwards compatibility. Turbocharger deposits were also identified as a growing concern, which EMA believes may result in a future need for an engine or a bench test. However, OEMs have no specific data at this stage.

Backward compatibility a tricky issue due to parts availability

Backward compatibility seems to be a tricky issue with several engine tests at risk due to parts availability. The Mack T-11 Engine Lubricant Test that is utilised in API CK-4 and API FA-4 is unlikely to be available for PC-12 and there is no obvious replacement test to measure soot-related viscosity increases. The Mack T-11 is a 252-hour test to evaluate the viscosity increase and soot concentration in a turbocharged, intercooled engine equipped with exhaust gas recirculation. The API Category Life Oversight Group (CLOG) is investigating the potential impacts on viscosity and backwards compatibility.

CLOG provided an update on potential impacts during a subsequent meeting of the NCET on October 19. During the presentation, CLOG emphasised that a replacement test will be required to license existing C categories. CLOG has eliminated so options and continues to pursue others. The Cummins ISM and ISB tests produce nearly as much soot as the Mack T-11CLOG is suggesting a comparison between the viscosity increase at given soot levels in Cummins ISM and ISB. ACC PAPTG has been asked to collate their data comparing the Mack T-11, Cummins ISM, and Cummins ISB.

The Mack T-12 engine test evaluates the wear performance of an engine lubricant in turbocharged intercooled diesel engines equipped with exhaust gas recirculation (EGR) and operating on ultra-low sulphur diesel fuel. Based on EMA surveys, the trade association believes a replacement test for the Mack T-12 is not necessary for PC-12. If a wear concern is identified during the category development process regarding characteristics that are currently covered by the Mack T-12, such as liner wear and top ring mass loss, EMA recommended adjusting the limits of an existing test rather than developing a new test.

Licensing existing C categories

However, CLOG has indicated the need for a replacement test to license existing C categories, and there is no current wear test that provides sufficient ring or liner wear. The oversight group also highlighted the need for lead and oil consumption parameters in API CH-4, API CI-4, and API CJ-4, stressing that no existing tests generate sufficient lead to replace the Mack T-12 engine test.

The high-soot engine Roller Follower Wear Test (RFWT) is used to evaluate how effectively lubricants limit axle wear in the roller cam lifter. Initially considered doubtful for PC-12, EMA indicated that RFWT is not needed for the new category. EMA also confirmed the Detroit Diesel DD13 Engine Scuffing Test is available for PC-12, and recommends it for the F category only. The Ford 6.7L Valve Train Wear (VTW) test should be considered for additional wear needs for PC-12. These two parameters are not currently in API CK-4.