Unplanned maintenance for a disabled truck is one thing that fleet owners never want to deal with, a problem that can lead to a domino effect of inconveniences and costs. If paid per mile, your truck’s driver may be temporarily unable to earn his or her living. Additionally, a sidelined truck is an unprofitable one, and its cargo will likely not make it to its destination on time. Meanwhile, the fleet manager must coordinate a tow and repair, which by itself can be expensive.

Maintenance costs like these have consistently made up between 8 and 10% of a fleet’s average cost per mile over the past ten years, according to a recent report from the American Transportation Research Institute (ATRI), “An Analysis of the Operational Costs of Trucking: 2020 Updates.” Bearing this in mind, it’s no wonder that fleet owners do everything in their power to protect their trucks from unforeseen breakdowns.

To those ends, regularly servicing trucks with high-performance engine oil is one effective way that fleet managers can minimize downtime. But not all heavy-duty engine oils are created equally, and some choices available today can provide benefits beyond baseline engine protection.

Here’s what you should know, and why choosing a lower-viscosity lubricant can impact your bottom line.

Through thick and thin

In 2016, the American Petroleum Institute (API) made a fundamental change in how heavy-duty engine oils are certified for use throughout North America. In addition to introducing the new CK-4 category, API introduced FA-4— leading to a split category for low-viscosity engine oils, with FA-4 being specifically formulated to deliver enhanced fuel economy benefits for modern engine hardware (model year 2017 and newer) via less resistance between moving engine parts.

Per API requirements, both CK-4 and FA-4 oils deliver the same levels of high performance and engine protection. But to date, market share of FA-4 hovers only around 1%, while approximately 79% of diesel lubricants sold in the North American market are 15W-40, according to data from Kline Lubesnet. No other available grade breaks the 10% threshold.

Why has this remained the case? It is in part because traditional market wisdom has long held that higher-viscosity lubricants can better protect engines than lower-viscosity lubricants—an assumption that has been proven incorrect with the advent of properly formulated low-viscosity grades and rigorous testing. In fact, Lubrizol has field-tested FA-4 lubricants in real-world engines from a variety of OEMs, generating over 86 million miles of testing. Trucks we’ve tested include new models designed to be filled with FA-4 lubricants, and older-model trucks where FA-4 is not specified by the manufacturer. Through this testing, what we’ve found is clear: Engines, old and new, are demonstrating normal wear levels at up to 500,000 miles of service while demonstrating significant fuel economy improvement.

It is additionally worth keeping in mind that many heavy-duty truck OEMs today factory-fill most new-model engines with 10W-30 grade lubricants, a choice that highlights their confidence in lower viscosities. So, if you’ve continued to use 15W-40 lubricants in newer trucks, switching viscosities is a choice worth investigating, if only to remain consistent with your OEM’s specification. Engines that have been designed to operate with a certain lubricant viscosity grade should be filled with that grade during regular service.

Seizing fuel economy benefits

The real advantage of lower-viscosity lubricants lies in their ability to deliver fuel economy benefits.

Consider first that fuel costs are a prime target for a cost reduction for fleet owners, representing approximately 24% of a fleet’s average cost per mile, according to the ATRI Trucking Review. Lower-viscosity formulations can help here: According to “Trucking Efficiency Confidence Report: Low-Viscosity Engine Lubricants,” a joint report from the North American Council for Freight Efficiency and Carbon War Room, the benefits of upgrading to available low-viscosity lubricants are clear cut. “Class 8 over-the-road fleets can realistically expect fuel savings in the range of 0.5%-1.5% by switching from 15W-40 to 5W/10W-30 engine oil,” the report says.

FA-4 lubricants provide even greater benefits when used in the appropriate engine. According to the same report, “The savings from switching to the fuel-efficient FA-4 variant … can be expected to add a further 0.4%-0.7% of increased fuel efficiency.” Projected across the lifetime of the vehicle, which may see more than a million miles on the road before it is taken out of service, FA-4 has the potential to deliver some dramatic fuel cost savings versus a more conventional lubricant choice. Projected across an entire fleet, the numbers add up even higher.

Ready to make a change?

Selecting a new engine oil for your fleet is a major operational decision, and it should involve close conversation with your oil supplier before making the switch. You may want to consider performing some initial field-testing to gauge how a lower-viscosity solution can impact your specific operational requirements. Since long before the development of CK-4 and FA-4 specifications, Lubrizol has been working carefully with OEMs and oil marketers to formulate lower-viscosity engine oil solutions that provide robust engine protection with carefully selected additive chemistry. We’re ready to support everyone in our collective journey into the low-viscosity future.

This article was contributed by Greg Matheson, product manager for heavy duty engine oils with The Lubrizol Corp.