Unlocking fuel efficiency: The rise of low-viscosity oils in HDD engines

The American Truck Dealers (ATD) reported a 3.8% increase in commercial truck sales, reaching 476,000 units, in 2022. As a division of the National Automobile Dealers Association (NADA), ATD represents nearly 5,600 separate franchises, both domestic and import. The upward trajectory in sales is expected to continue into 2023, particularly for medium-duty trucks.

However, a slight decline is anticipated in the sales of Class 8 trucks, vehicles with a gross vehicle weight rating (GVWR) exceeding 33,000 pounds. These trucks, which predominantly run on diesel, are pivotal in the transportation and construction sectors and are increasingly becoming a focal point for environmental sustainability initiatives. The transition towards eco-friendly alternatives is evident. A growing inclination towards natural gas and electric fuel options is emerging amidst the predominant use of diesel in Class 8 trucks. This shift is propelled by the intensified focus on curtailing greenhouse gas emissions (GHG) and enhancing fuel efficiency.

In light of this, the U.S. Environmental Protection Agency (EPA) unveiled a proposal on April 12, 2023, outlining more rigorous standards to mitigate greenhouse gas emissions from heavy-duty vehicles, effective from the model year 2027. The proposed “Phase 3” program aims to enforce progressively stringent CO2 standards through 2032, building on the flexible structure established in the Phase 2 program.

Amidst these environmental regulatory advancements, a notable evolution is occurring in the heavy-duty diesel engine oil market. The longstanding reliance on SAE 15W-40 is giving way to a preference for lower viscosity engine oils. Recognising the fuel-saving benefits, original equipment manufacturers (OEMs) are increasingly endorsing these low-viscosity engine oils.

The American Petroleum Institute (API) introduced API CK-4 and FA-4 in December 2016 to accommodate the emerging needs for fuel economy and emissions reduction. These categories offer enhanced engine oil aeration, wear and deposit protection, oxidation control, and shear stability compared to their predecessor, API CJ-4.

API is also in the midst of developing Proposed Category 12 (PC-12) to address the requirements of the upcoming EPA regulation. OEMs are working to achieve more fuel economy improvements for PC-12. 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 of oils with lower viscosity than those available in API FA-4, the API service category which describes certain XW-30 oils specifically formulated for use in select high-speed four-stroke cycle diesel engines designed to meet 2017 model year on-highway GHG emission standards.

The shift towards SAE 10W-30 is anticipated to gain momentum, potentially accounting for approximately 40% of the heavy-duty diesel (HDD) market by 2029. Although the adoption of even lower SAE XW-20 viscosity grades is expected to be gradual, contingent on further innovations by HDD OEMs.

The transition to low-viscosity heavy-duty engine oils is underscored by tangible benefits, including reduced GHG emissions and significant fuel savings. Despite the reservations of some HDD fleet owners, the evolution towards these oils is inevitable, given the design of newer truck engines for enhanced fuel economy and friction protection.

Low-viscosity engine oils are not just a trend but a reflection of the industry’s commitment to balancing engine protection and environmental preservation. These oils promise enhanced engine performance, versatility in application, and approval by leading engine manufacturers.

As the automotive landscape grapples with the dual challenge of reducing CO2 emissions and boosting fuel economy, the gravitation towards lower viscosity engine oils is not just inevitable but essential. For fleet operators, engaging in informed dialogues with suppliers about this transition can unlock both environmental and economic dividends, marking a significant stride towards a sustainable automotive future.

By Steven Bowles, Certified Lubrication Specialist and Oil Monitoring Analyst I, CITGO