What Are API Standards For Motor Oil and Why Are They Important?

The American Petroleum Institute (API) sets standards for motor oil to help consumers and mechanics choose the correct oil for their vehicles based on engine type and year of manufacture. These standards are designated by two-letter codes — beginning with “S” for gasoline engines and “C” for diesel engines — followed by another letter that represents the oil’s performance level. Here is a short guide on API motor oil standards.

Gasoline Engine Standards (S-series)

• SA to SH (Obsolete: 1930s–1990s): SA, SB, and SC were for non-detergent and minimal detergent oils, offering little protection by today’s standards. SH, introduced in 1992, brought improvements in wear protection, sludge control, and high-temperature stability.

  
  

• SJ (1996): Enhanced oxidation control and improved performance in higher RPM engines. Now obsolete in many contries.

  SL (2001): Developed for 2001 and older engines. Improved deposit control, wear protection, and oil longevity. Obsolete in some countries but still found in some legacy oils.

  
  

• SM (2004): Introduced better oxidation resistance and low-temperature performance. Obsolete in some countries.

  
  

• SN (2010): Designed for 2011 and older engines. Introduced protection against high-temperature deposits and sludge. Still in use, though superseded.

  
  

• SN Plus (2018): Addressed issues like low-speed pre-ignition (LSPI) in turbocharged gasoline direct-injection engines. Obsolete as it has been rolled into SP.

  
  

• SP (2020): The current standard for gasoline engines. Offers improved wear protection, low-speed pre-ignition (LSPI) resistance, and protection for turbocharged engines.

  
  

Diesel Engine Standards (C-series)

• CA to CH-4 (Obsolete: 1940s–1998): These earlier classifications progressively introduced improvements in soot control, wear protection, and oxidation stability.

  
  

• CI-4 (2002): Introduced for high-speed, four-stroke engines using exhaust gas recirculation (EGR). Offers enhanced protection from soot-related wear. Still used in most applications.

  
  

• CJ-4 (2006): Developed to meet 2007 emissions standards with particulate filters. Improved engine cleanliness and durability. Mostly obsolete.

  
  

• CK-4 (2016): Current standard. Provides high-temperature stability and protects emission control systems. Compatible with both older and newer engines.

  
  

• FA-4 (2016): Similar to CK-4 but designed for newer, fuel-efficient engines requiring lower high-temperature high-shear (HTHS) oils. Not backward-compatible with all older engines.

As engine technologies and regulatory requirements continue to evolve, so do the API standards. Using the right API classification ensures optimal engine performance and longevity. As always, it is best to consult your owner's manual to determine the correct API rating for your engine. To get the right engine oil for your car, contact us to find a dealer near you or visit the AutoPerformance Lazada or Shopee official stores to shop online. For dealership inquiries, contact us.