What are the two main categories in the API classification system for oils?

The API classification system for motor oils primarily divides oils into two main categories: "C" for commercial engine oils and "S" for spark ignition engine oils. This classification system helps consumers, technicians, and manufacturers identify the appropriate oil based on the engine type and its performance needs.

The "C" category is designed for diesel engines and emphasizes performance characteristics that protect against soot and higher levels of contamination typically found in commercial use. In contrast, the "S" category is focused on oils that are formulated for gasoline engines, ensuring they meet the necessary requirements for engine longevity under typical operating conditions.

This clear categorization facilitates easier selection of the right oil for various engine types, ensuring optimum performance and protection. Understanding these categories is crucial for anyone involved in automotive maintenance and oil changes, as selecting the wrong type of oil can lead to subpar performance and potential engine damage.