There’s a lot of talk in our oil drain interval and used oil analysis story about manufacturer-set oil drain intervals. And you may be wondering: how do they set those intervals, anyway?

“During the design and development phase of our engines, we run thousands of test hours and hundreds of thousands of miles in field tests to understand how the engine interacts with the oil,” explained Corey Trobaugh, corporate materials science and technology leader for Cummins.

“As an engine operates, oil chemistry changes. Acidity increases, and when it exceeds a certain level, damage can occur to bearings and seals, reducing engine longevity. The viscosity of oil also increases, which reduces fuel economy,” said Jim Nachtman, on-highway product marketing director for International Trucks. “Wear metals and contaminants accumulate in the oil filter, and require an oil filter change to ensure that adequately filtered oil flows through the engine.”

According to Dan Arcy, global OEM technical services manager for Shell Lubricants, factors considered by the OEMs in setting the intervals include the amount of contamination that is going to get in the oil from things like byproducts of combustion, fuel dilution, dirt, etc.

Of course, depending on your engine extending the drain interval might not be necessary at all. Jason Johnson, director of aftermarket for PACCAR Inc., touted the PACCAR MX engines’ oil drain interval of 75,000 miles for line-haul applications, saying that “PACCAR MX engines are rigorously tested in a wide variety of operating conditions and environments with extensive oil sampling and data analysis. This leads to very high confidence in the published service intervals that fleets should use to maximize uptime and minimize the cost of maintenance.”