What is the API service category classification system?
Engine oils are currently classified by a two-letter code. Gasoline engine oil categories start with the letter S (originally designated “Spark Ignition” engine oils, we now associate the S with “Service”). Diesel engine oil categories start with the letter C (originally designated “Compression Ignition” engine oils, we now associate the C with “Commercial”). The second letter is simply a sequential designation of improving quality levels over time. In other words, when a new industry quality level is established, the next letter of the alphabet is used (so SJ replaces SH). The letters “I” and “K” were purposefully skipped to eliminate potential confusion with other commonly used designations.
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- What is the API service category classification system?
