Lower viscosity, lower costs? How engine oils impact cost per mile

As fleets face rising operating costs, maintenance managers are under pressure to control cost per mile without sacrificing uptime. Lubrication choices, engine oil viscosity in particular, may seem incremental, but they can have a large impact on fuel economy, service intervals, and overall operating costs.

Engine oil is one area where fleets can seek real cost-per-mile savings, without compromising quality or reliability.

NACFE research 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 improvement. When switching to an FA-4 10W-30, fleets could see another 0.4-0.7% improvement.

Sounds like a no-brainer, yet NACFE says adoption of lower-viscosity engine oils is still rather low, perhaps 20% industrywide. One reason for that is the price premium, as lower-viscosity synthetics and synthetic blends often cost 30-40% more than conventional 15W-40s.

But what is the real impact on CPM? With all things considered—price of the oil, oil drain interval, and fuel economy—the lower-viscosity synthetics could provide a financial advantage over the less expensive conventional 15W-40s.

Consider the following hypothetical example:

• $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, respectively
• Engine oil CPM comes out to $0.002875, $0.0025, and $0.003, respectively
• Base fuel economy with a conventional 15W-40 is 8 mpg, 1% improvement (average) 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 $3.75
• Fuel CPM using conventional 15W-40 is $0.469, CK-4 10W-30 synthetic is $0.464, and FA-4 10W-30 synthetic is $0.462
• Total CPM (oil + fuel) is $0.4719, $0.4665, and $0.465, respectively

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 $486 a year, and using an FA-4 10W-30 synthetic could save another $133—even though those oils will likely cost more upfront to purchase.

CITGARD 700 MFE Synthetic Blend is an FA-4 10W-30 heavy-duty engine oil that’s formulated with advanced base oils and friction‑modifying additives that create a thinner, stable lubricating film that maintains its viscosity in High-Temperature, High-Shear (HTHS) environments. The oil flows quickly at startup and minimizes energy losses as engine parts move against each other. CITGO says the typical fuel economy improvement is 1-3%, as compared to a conventional 15W-40. 

Meanwhile, the company offers SynDurance Synthetic MTF (Manual Transmission Fluid)that claims to improve fuel economy by 0.5-1.5%. CITGO said this is achieved by reducing internal friction and improving power transfer efficiency as compared to conventional transmission fluids.

Another thing to think about is the impact on technician labor costs by extending out those drain intervals with the synthetic 10W-30s.

For example, Valvoline’s Premium Blue One Solution Gen 2, an 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 that equipment can spend more time on the job and less time being serviced,” noted John Walters, Valvoline’s GM and VP for the Heavy Duty Americas channel. “This is an enormous benefit to operators looking to maximize their capital investments.”