While the novice may think the quality of oil coming from any plastic industrial container is above reproach, experienced operators and fleet owners know not to take any oil for granted. The type of oil being used in any freight or construction vehicle can have a huge impact on fuel savings and engine upkeep. That’s why a recent report revealing that using lower viscosity engine oils can increase fuel savings is so important.

Truck owners who switch to lower viscosity engine oils can increase fuel savings by as much as 1.5 percent, the study found. That’s only an average, though, according to a new Confidence Report from the North American Council for Freight Efficiency (NACFE) and Carbon War Room. Some estimates reported by fleets, perhaps reflecting other best practices, were quite higher.

Viscosity – One Key to Engine Performance

Why is viscosity – defined as a measure of a fluid’s internal resistance to flow – so important? It is the single most critical physical property of the oil as it affects both the wear rate and the fuel efficiency of the engine.

Think of it as the difference between water (low viscosity) and syrup (high viscosity). Inside a truck’s engine, mechanical losses from pumping and friction consume approximately 16 percent of the total energy input to the vehicle. Using lower-viscosity oil will reduce that energy expense on the engine, thereby reducing fuel use to keep the engine running.

In December, the introduction of a new PC-11 engine oil performance category will result in the largest change in oil specifications the trucking industry has seen in decades.

Lower Viscosity = Higher Fuel Savings

The report revealed that 5W-30 and 10W-30 engine oils, either the current CJ-4 or the upcoming CK-4 under the new standard, can replace the commonly used 15W-40 oils and increase fuel savings by between .5 and 1.5 percent. NACFE’s researchers also reported that that the FA-4 variant of the new PC-11 oils can add an extra 0.4 to 0.7 percent fuel savings on top of the CJ-4 or CK-4 oils. The “backward compatibility” of the new standard oil remains a major unknown, the study stressed.

“Fleets don’t want two oils in their systems: we heard that loud and clear in our interviews,” Mike Roeth, the group’s executive director explained. “So we hope to see work go on to approve these oils as far backward as possible.”

Roeth also told reporters that it “feels like we’ve got a tipping point here” in terms of getting the trucking industry to switch to lower viscosity oils.

“The old axiom that heavier oils will protect my engine better is falling apart now,” Roeth said. “I went in with the assumption that FA-4 would not be “backward compatible”. But as we start testing older engines with the newer [FA-4] oils, it may be. I expect there to be a growing amount of test data on this.”

Fleet owners thinking about switching to lower viscosity oil need to keep several factors in mind, according to NACFE:

• For fleets using non-synthetic 15W-40 oils there is a cost entailed in switching to low-viscosity engine oil, largely due to the fact that much of the 15W-40 oil found on the market today is mineral-based;
• At the retail level, a switch from mineral-based oils to synthetic blends typically increases cost by 30% to 40%, even within the same brand family. Therefore, a higher price for engine oil will increase maintenance costs over the lifetime of the switch.
• Yet NACFE’s research also found switching to lower-viscosity oil may allow a fleet to consider an extended drain interval, which can help offset that price premium.
• Although the ability to extend drain intervals varies greatly by various factors such as duty cycle, one fleet that this study team interviewed extended its drain interval by 20,000 miles by switching to lower-viscosity oil.