Oil Classifications Diesel and Gasoline Engines

Oil Classifications Diesel and Gasoline Engines

Oils are generally classified as refined and synthetic. Paraffinic and naphthenic oils are refined from crude oil while synthetic oils are manufactured. Literature on lubrication frequently makes references to long chain molecules and ring structures in connection with paraffinic and naphthenic oils, respectively. These terms refer to the arrangement of hydrogen and carbon atoms that make up the molecular structure of the oils. Discussion of the chemical structure of oils is beyond the scope of this webpage.

The current and previous API Service Categories are listed below. Vehicle owners should refer to their owner’s manuals before consulting these charts. Oils may have more than one performance level.

For automotive gasoline engines, the latest engine oil service category includes the performance properties of each earlier category. If an automotive owner’s manual calls for an API SJ or SL oil, an API SM oil will provide full protection. For diesel engines, the latest category usually – but not always – includes the performance properties of an earlier category.