For some of us with gray in our hair, it seems like only yesterday when most motor oils were labeled for use in both passenger cars and diesel trucks. That was back in the 1980s and earlier, when motor oil claimed both API Service (S) and Commercial (C) performance categories. These products were considered universal in that they could be used in both gasoline and diesel engines.
As an example, I have an old can of Texaco Ursa LA-3 SAE 30 oil from the early 70s that states its For both Diesel & Gasoline Engines operating under light to heavy duty service conditions…for Stop-and-Go Driving, High Speed Highway Driving. For Construction Equipment under heavy loads & Marine Engines. Next to it is a Shell Oil pocket calendar from 1963 showing a can of Shell Rotella T accompanied by the statement NOW… for MIXED FLEETS with gasoline and diesel engines. One engine lubricant for all trucks and buses, all seasons, all types of service. And there are many others.
Buying motor oil was fairly easy back then because, whether for gasoline or diesel engines, the API S and C categories were joined at the hip, and there were only a few viscosity grades to select from. If it was good for gasoline engines, it was good for diesels. This was certainly convenient for fleets operating both types of vehicles.
The S and the C categories started to part ways in the 1990s, for several reasons. One was due to limits on phosphorus content ushered in with the International Lubricant Specification Advisory Committees GF- series of specifications. Long story short, in an effort to address fuel economy and catalyst life, GF-2 required PCMO to contain about 20 percent less of the workhorse antiwear additive ZDDP. It dropped another 20 percent along the way as we moved to the current GF-5. Although this helped resolve catalyst compatibility issues, the skinnied down levels of ZDDP became an issue for heavy duty diesel engines and reportedly some older cars on the road with flat tappet valves.
In addition, over the years PCMO has been moving to lower levels of detergents and dispersants in an effort to improve fuel economy. While this has achieved its goal, it has also widened the gap between gasoline and diesel engine oils.
Viscosity is another reason for the divergence. Even though both cars and trucks formerly used similar viscosity grades, Corporate Average Fuel Economy requirements moved U.S. passenger car manufacturers to specify such lighter grades as SAE 5W-X, and now 0W-X. In the minds of many fleet operators and engine builders, these viscosity grades are too light for use in heavy duty applications.
To further the separation, divisions also occurred within the world of heavy duty engine oil when specifications split to accommodate engines running on low- and high-sulfur fuel, and with and without exhaust gas recirculation. Fleet managers are now looking at API CH-4, CI-4, CI-4 PLUS and CJ-4 as the current categories for HDEO, and API SN/ILSAC GF-5 for their gasoline engines.
As you can see, the engine oil requirements for gasoline and diesel engines parted ways in the 90s, and selecting engine oils became much more complicated. You can be sure that is not what fleet operators wanted. In fact, much of the market research Petroleum Trends has done over the years continues to find that the Holy Grail for fleet operators is a one-barrel engine oil solution that meets the specifications of all of their diesel and gasoline engines.
Understanding this, there is little wonder why we again see engine oils on the shelves sporting both API C and S, and some that claim to be universal. At the same time, if you look closely at the labels on these products, its important to consider that makers of passenger cars and light trucks recommend not just the API S claim, but also the ILSAC starburst – which is never seen on heavy duty diesel lubricants.
Even so, there is a good chance we may see more universal motor oils on the market as heavy duty OEMs and diesel fleet operators move to lower viscosity grade products in an effort to capture fuel economy. But even if viscosity recommendations for diesel and gasoline engines once again merge, can universal motor oils really meet the needs of all cars and trucks on the road?
According to some of the additive and lubricant manufacturers I speak with, there is little to no chance of this, in part because some of the specifications are mutually exclusive. Further, if a motor oil could meet the specifications for both gasoline and diesel engines currently on the road, it would at best be a compromised product. Thats because the soot handling, shear stability, oxidation stability, detergency, antiwear, exhaust aftertreatment, and other requirements are too different now for diesel and gasoline engines.
Are consumers and fleet operators willing to accept compromises for the convenience of simplicity, or are they willing to pay significantly more for motor oils that offer convenience with no compromises? Can there even realistically be a universal diesel oil good for old and new diesel trucks, or a universal gasoline engine oil good for all gasoline engines? With the growing complexity, it seems more and more unlikely.
Tom Glenn is president of the consulting firm Petroleum Trends International, the Petroleum Quality Institute of America, and Jobbers World newsletter. Phone: (732) 494-0405. E-mail: tom_glenn@petroleumtrends.com