Every time a new class of diesel engine oil comes out, prices seem to creep up a little. But formulations also improve, providing enhanced engine protection, which can sometimes lead to longer drain intervals and reduced engine maintenance. Oil viscosity also tends to creep down a notch, which can lead to improvements in fuel economy.

Research from the North American Council for Freight Efficiency (NACFE) shows that lower-viscosity oils with less internal resistance to flow will reduce mechanical losses, thereby reducing fuel use. In fact, switching from 15W-40 to 10W-30 often results in a 0.5-1.5% fuel economy gain, on average. When switching to an FA-4 10W-30, fleets could pick up another 0.4-0.7%.

Still, after nearly a decade on the market, adoption of lower-viscosity engine oils is only around 20% industrywide, according to NACFE. The price premium is one reason, as lower-viscosity synthetics and synthetic blends often cost 30-40% more than conventional 15W-40s.

But what is the total impact on cost per mile (CPM)? When considering the price of the oil, the oil drain interval, and fuel economy, could lower-viscosity synthetics actually provide a financial advantage over the less-expensive conventional 15W-40s?

Let’s look at the numbers using the following hypothetical scenario:

• $115 for 40 quarts of conventional 15W-40, $150 for a CK-4 10W-30 synthetic, and $225 for an FA-4 10W-30 synthetic.
• Oil drains are 40,000, 60,000, and 75,000 miles.
• Engine oil CPM comes out to $0.0029, $0.0025, and $0.003.
• Base fuel economy with a conventional 15W-40 is 8 mpg, 1% improvement for a CK-4 10W-30 synthetic bumps mpg to 8.08, then another 0.55% improvement when using an FA-4 10W-30 synthetic bumps mpg to 8.12.
• Diesel fuel is $5.65 per gallon (as of May).
• Fuel CPM using conventional 15W-40 is $0.706, CK-4 10W-30 synthetic is $0.699, and FA-4 10W-30 synthetic is $0.696.
• Total CPM (oil + fuel) is $0.7091, $0.7018, and $0.6988.

Given all of that math, and assuming a truck puts on 90,000 miles over the course of a year, using a CK-4 10W-30 synthetic could save around $657 a year. Using an FA-4 10W-30 synthetic could save another $270—even though those oils will likely cost more up front to purchase.

Longer oil drain intervals can reduce technician labor costs

Another thing to consider is the possibility of further reducing repair and maintenance (R&M) cost by extending drain intervals with the synthetic 10W-30s, especially an FA-4. Eliminating an oil change each year will reduce technician labor, which helps drive R&M even lower. There’s also the financial impact of increased uptime to consider.

As an example, Valvoline’s Premium Blue One Solution Gen 2, a CK-4 oil suitable for diesel, gas, and natural gas, was approved by Cummins for 100,000-mile oil drain intervals in the current X15 engine. “This milestone means equipment can spend more time on the job and less time being serviced,” John Walters, Valvoline’s GM and VP for the Heavy Duty Americas channel, said.

Ken Eggen, an industry veteran who now has a maintenance consulting business, K.M.E. Services, said ROI will largely hinge on a fleet’s ability to achieve its desired drain cycle. That’s not always a guarantee.

“If a fleet cannot execute PMs (preventive maintenance) on time and use oil analysis consistently, I would be very cautious about assuming something like a 75,000-mile drain interval,” Eggen said. “The risk is that the fleet buys premium oil but still operates with ordinary maintenance discipline.”

Foodliner extends oil drain intervals to reduce fleet maintenance costs

Kyle Neumann started running FA-4 10W-30 oils as soon as they became available in December 2016. His long relationship with Citgo gave him the confidence to make the switch to Citgard 700 MFE Synthetic Blend.

As the VP of maintenance for McCoy Group’s Foodliner and Quest Liner brands, Neumann wasn’t motivated by fuel economy because his fleet of tanker trucks racks up a lot of idle and PTO time. The driving force behind Neumann’s decision was the potential cost savings associated with more than tripling his current oil drain interval (ODI).

“When we went from a 24,000-mile (90-day) oil drain to 48,000 (180 days), we cut costs by more than $300 per truck,” Neumann explained. “Then when we extended to 72,000 miles, the savings doubled.”

The savings continued to grow once Neumann’s team extended out to 90,000 miles. And it’s not just about getting significantly longer life out of 40 quarts of oil.

“With the tight technician workforce we have today, I have to take a look at anything I can do to drive efficiency and capacity in our shops,” Neumann said. “We’re essentially doing one wet PM a year now. That has had a huge impact on our shop throughput because technicians have more time for other services.”

Trucks still come in for dry PMs at 45,000 miles (170 days) to make sure everything is getting inspected and greased as required. Oil sampling has also become a key task during those dry PMs, as well as the 90,000-mile wet PM.

“One of the keys to extending ODIs like we have is that we watch oil samples like a hawk,” Neumann related. “We’ve actually set up a specific PM code in our maintenance software just for pulling oil samples. That way it’s easier to track them and make sure they’re getting done.”

Could PC-12 engine oils lower fleet cost per mile?

Now the question is whether the new PC-12 oils (CL-4 and FB-4) that will be arriving next year will be capable of further reducing CPM.

Like the CK-4 oils they are replacing, CL-4 will be offered in 10W-30 formulations. A new CL-4 might not improve fuel efficiency but could still help lower CPM.

“Many factors contribute to reducing cost per mile,” Karin Haumann, OEM technical manager at Shell Global Solutions, explained. “PC-12 oils are being developed to extend oil drain intervals and increase the durability of aftertreatment systems, which can help reduce cost per mile.”

Fuel economy gains are expected with the new FB-4 oils. They will be available not only as 10W-30s but also lower viscosities like 0W-20 and 5W-20. Some estimates suggest fuel economy gains in the 0.5-1% range when using a 20-weight, as compared to FA-4 10W-30s. Exact oil drain intervals remain to be seen.

The price of these new CL-4 and FB-4 oils also remains to be seen. They won’t be commercially available for several more months, so oil marketers are understandably reluctant to talk about pricing. Due to the advanced formulations of these new oils, conventional wisdom suggests they will carry a price premium over the CK-4s and FA-4s they replace.

The question for fleets is whether any price premium could be offset by the benefits of using a more advanced engine oil.

Let’s use the same formula from earlier to draw a hypothetical comparison between an existing FA-4 10W-30 and a looming FB-4 20-weight. We’ll assume the FB-4 costs 35% more, gets 0.75% better fuel economy, and has a 10% longer drain interval. In that scenario, a 20-weight FB-4 could help a fleet lower CPM by 0.45 cents per mile. Over the course of a year and 90,000 miles, that could help a fleet save a little more than $400 per truck.

Keep in mind that the $400 per-truck savings isn’t counting any potential reduction in technician labor cost by extending drain intervals nor any potential engine and aftertreatment maintenance savings resulting from increased system performance. If a fleet saw some gains in those areas, CPM could still come down if the price of a looming FB-4 oil was triple an FA-4.

At the end of the day, it’s important to remember that certain engine oils can help improve fuel economy and extend oil drains, but their primary job is to protect the engine. That’s another check in the column for advanced engine oils, despite their higher upfront cost.

“The correct viscosity grade will depend on the engine design, duty cycle, and OEM approval language,” Bill O’Ryan, EOLCS/DEF director at the American Petroleum Institute (API), said. “The cost-per-mile advantage comes when a lower-viscosity oil is matched to an engine designed to use it while still delivering the wear protection, oxidation control, and aftertreatment compatibility that’s required.”