80% of fleets, according to Arcy, use 15W40 engine oil, a multi-grade lubricant with low and high temperature performance characteristics.

10W30 oil is lower in viscosity, meaning it is “thinner” and flows more readily. Some engine manufacturers restrict the use of lower viscosity oils for certain engines and in specific ambient temperatures. For example, engine builders may limit the use of a 10W30 lubricant if temperatures in a fleet’s main operating area go above 86˚ F.

“Fuel efficiency improvement is possible with a lower viscosity oil,” Arcy says, “but it’s important to check with the engine manufacturer before making the decision to switch.”