CK-4, FA-4? Still Confused About Diesel Engine Oil Specs?

CK-4, FA-4? Are you still having diesel engine oil confusion? Consider this post simply as a tutorial about the differences between the current diesel engine oil standards known as American Petroleum Institute’s (API) CK-4 and FA-4. These service categories came out a few years ago as an improvement over the previous API Diesel Engine Oil Standards by providing enhanced protection against oil oxidation, engine wear, particulate filter blocking, piston deposits, and degradation of low- and high-temperature properties.

API CK-4 describes oils for use in high-speed, four-stroke diesel engines designed to meet 2017 model-year on-highway and Tier-4 non-road exhaust-emission standards as well as for previous model-year diesel engines. That is, they are backward compatible.

These oils are formulated for use in all applications with diesel fuels ranging in sulfur content up to 500 parts per million (ppm). However, the use of these oils with greater than 15 ppm sulfur fuel may impact exhaust aftertreatment system durability and/or oil drain intervals.

CK-4 oils exceed the performance criteria of API CJ-4, CI-4 Plus, CI-4, and CH-4, and can effectively lubricate engines calling for those service categories. When using CK-4 oil with higher than 15 ppm sulfur fuel, consult your original engine manufacturer (OEM) for service interval recommendations. Most diesel OEMs are recommending you use API CK-4 oils as a replacement going forward.

The API FA-4 standard designates certain lower viscosity oils specifically formulated for use in select high-speed, four-stroke diesel engines designed to meet 2017 model-year on-highway greenhouse gas (GHG) emission standards. Diesel OEMs are recommending this new oil spec for most late model-year engines. These oils are neither interchangeable nor backward compatible with API CK-4, CJ-4, CI-4 Plus, CI-4 or CH-4 oils. Therefore, you should follow the OEM’s advice when they recommend API FA-4 oils.

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