Fuel and repairs make up a large chunk of a trucking company’s budget. According to a study published by the American Transportation Research Institute, between 8% and 10% of a fleet’s average marginal cost per mile is spent on maintenance and repairs. Fuel costs represent between 21% and 39% of the cost per mile. Making the right choice of engine oil can reduce these costs. This isn’t thanks to some new additive or chemical advance. It’s because the North American trucking industry has mostly ignored established standards and practices.

In 2016, the American Petroleum Institute (API) introduced new certifications to keep up with new lubricant and engine technologies. CK-4 and FA-4 certifications have better oxidation control, shear stability, and aeration performance. This helps these new oils last longer and lubricate better under all operating conditions. Using these engine oils reduces fuel consumption and wear, which leads to breakdowns. However, these oils have different purposes. CK-4 replaced CJ-4, offering improved performance while being backward compatible with earlier standards. The FA-4 standard was designed with 2017 and later truck engines in mind. These newer engines run hotter than previous engines, so FA-4 oils have a lower high shear viscosity range at high temperatures. This reduces friction under normal operating conditions, delivering better fuel efficiency than CK-4.

Currently, 79% of heavy-duty diesel oil sold in North America is CK-4 15W-40. The next most popular oil is CK-4 10W-30, at 9% of the market, while just 1% of oil sold is FA-4 grade. There is a mistaken belief that higher viscosity oils are better at protecting engines, despite 10W-30 lubricants being the standard factory fill for most truck engines. A combined report by the North American Council of Freight Efficiency and the Carbon War Room found that Class 8 fleets can expect a fuel savings of 0.5 to 1.5% by switching from 15W-40 to 5W-30 or 10W-30 oil. Switching from CK-4 to FA-4 oil in newer trucks can increase fuel efficiency by 0.4% to 0.7%. Price differences between oils are negligible, making this one of the easiest ways to save operating costs.