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Commercial (Diesel) Oil

The additive packages for C (commercial) certification are designed to promote engine life. The additive packages for C rated oils contain extra buffers and detergents to keep the engine clean and free of acids. C rated oils are far better than S oils at holding and dispersing combustion byproducts and other contaminants, and at not becoming acidic. Traditionally these oils are primarily used in diesel motors, which are very expensive and are expected to last a million miles or more. When an engine rebuild costs $10,000 - $15,000 and puts you out of work for a week or three, you don't mind paying a bit more for your oil. The C certification tests have been largely developed by Mack, Caterpillar, Detroit and Cummins to provide the additives necessary to keep these engines running a long time. The latest commercial certification is CI-4 Plus, which includes extra protection for high temperature high revving motors. Since it's designed for diesel motors, they don't care about no stinkin' catalytic thingies, and CAFE is a place where you get a cup of joe and a donut. CI-4 Plus differs from CI-4 with higher detergent requirements and better sheer stability. The shear stability is exactly what motorcycles need due to running the engine oil through the transmission.

Although C standards are changed every few years, the older standards are enhanced, not superceded. So, newer higher rated C oils are simply better than older lower rated oils.

Although few car owners test their oil regularly, most large trucking companies routinely do oil analysis on their diesel trucks. Used oils are checked for viscosity breakdown, for detergent and dispersant function, and for metal contamination that would indicate engine wear. C oils that don't measure up are quickly run off the market place. To prevent engine wear, the best strategy is to keep deposits off the pistons, rings, and bearings. Therefore, diesel oils typically contain half again more detergents, double the dispersants, and a much more expensive and robust VII package than S type oils. If you go to an auto parts store, convenience store, or grocery store, you'll see that there are dozens of brands of automotive oils, all claiming to be the best. If you look at truck stops, you'll see there are only a very few diesel oils sold, typically Rotella, Delo, and Delvac. Trucking companies find what works for them and won't switch. They're not interested in saving a dollar a gallon on some unknown oil.

The C certified oils are all also S certified, just as some S certified oils are also C certified. The best C certified oils are SG, usually SH, sometimes SJ. I don't know of a C certified oil which is SL. The best S certified oils are CF, which is a relatively old and obsolete C standard, and does not include the tests for high speed high temperature engines that CG, CH, and CI have. In fact, CF oil does not meet the current factory standards for Volkswagen or Mercedes diesel passenger cars.

The API charges serious money to test an oil and certify it. If the API really tested the oil in their independent lab, and the oil company pays their royalties on time, the oil company gets to display the API seal on their product. Some smaller companies don't pay the API to test their oils and certify them. In these cases, you won't see the API seal, instead you'll see some words like "Meets or exceeds all manufacturers warranty requirements. API Service SJ, SL, CF." It's up to you to decide if you trust this manufacturer to actually test their oil themselves and tell you the truth about the results.

JASO certified Oil

Another institute that certifies oils is called the Japanese Automotive Standards Organization, JASO. One wonders why this Japanese organization has an English name. . . In any case, they have two classifications for motorcycles, "MA" and "MB." MA is the one you want. MB is like the API SL category, it's got all those nasty friction reducing chemicals that may scare your clutch into misbehaving. Again, there is an official JASO seal if the oil has been independently tested. The seal is a rectangle; in the upper quarter of the rectangle will be a serial number, and the lower three quarters will just have the letters MA. If the oil manufacturer did their own testing, instead you'll see just words like "Meets or exceeds JASO MA standards."

Some manufacturers recommend JASO-MA certified oil. AMSOil and Golden Spectro are JASO-MA certified. Some people consider this important. Interestingly, although Honda recommends a JASO-MA oil, Honda oil is not JASO-MA certified. Mostly JASO-MA is pretty much equivalent to SH. In fact, the JASO spec is mostly a reaction to the decrease in zinc-phosphates in SJ and SL oils, and the added molybdenum disulphide in energy conserving oils. Personally, I don't care about JASO standards - they're really not on my radar.

Racing Oil, NASCAR oil, etc.

Some manufacturers also sell something they call "racing oil." Normally, this is actually fairly decent oil, but you should not be mislead into thinking racing cars use the best oils for you. Race drivers start their engine one time only, warm it up slowly and carefully, then run the engine near or at the red line for a couple hours. 100 to 500 miles later, they completely tear down the engine and replace all the worn parts, the oil, and the oil filter. If you think you might like to go more than 500 miles between major engine rebuilds, you might consider that your use of your engine is quite different from Michael Andretti's.