Oil derivatives

What is the API grade of oil products?

The API grade of lubricating oil is a classification standard for the performance of internal combustion engine oils formulated by American Petroleum Institute (API), which is mainly used to represent the performance of lubricating oil in different types of engines, including gasoline engines and diesel engines. The API grade is one of the widely used lubricant performance classification standards in the world.

The API grades are divided into two main categories:

1. Class S (Service, Spark Ignition): Suitable for gasoline engines, which generally use spark plugs for ignition.

1. ⁠Class C (Commercial, Compression Ignition): Suitable for diesel engines, which are ignited by compression.

Specific meaning of the API grade

1. Class S (gasoline engine oil)

• Start with an “S”, followed by a letter (from “A” to the current latest “SP”).

⁠As increasing letters (e. g. SA→SB→SC), indicating the improvement of oil performance standards. The latest grade of lubricants is usually compatible with older grade engines, but not vice versa.

⁠Common grades include:

• SF, SG: suitable for older engines in the 1980s and 1990s.
• SL: For 2001 and previous engines.
• SN: Suitable for engines designed after 2010, with better high temperature oxidation resistance, deposition resistance and to meet the needs of turbocharged engines.
• SP (current latest, launch in 2020): Further optimized on the SN, specifically designed for modern efficient engines (such as turbocharged direct injection engines), with greater resistance to low speed pre-ignition (LSPI) and high temperature deposition.

1. Class C (diesel engine oil)
   Start with a “C”, followed by a letter (from “A” to the latest “CK-4”).
   The new grades are also generally compatible with the requirements of the older grade engines.

Common grades include:

• CH-4: Suitable to engines produced after 1998, comply with emission regulations.
• CJ-4: Suitable for engines produced after 2007, which meet more stringent emissions standards and are suitable for using lower sulfur content fuels.
• CK-4 (current latest): suitable for diesel engines after 2017, with more focus on high temperature, high shear stability and oxidation stability, while meeting more stringent emission standards.

How to select API grade oil products?

1. According to the engine manufacturer’s requirements: Select the API grade lubricant as recommended in the vehicle or equipment user manual.
2. ⁠Consider the engine using condition: For example, API SN or SP grade oil is recommended for modern turbocharged engines; for heavy-duty diesel engines, CK-4 is a better choice.
3. ⁠Pay attention to the compatibility of old and new grade: Generally speaking, higher API grade lubricants can be downward compatible with lower grade engines, but in some special cases, it is necessary to check that the additive formulation may affect the sealing materials of old engines.

Interactive question:
What is the difference between “SN” and “SP” in the API grade? If your engine is manufactured in 2015, which API grade oil will you choose?