What Does the Oil Number Represent?

[DeLucille]

Oil numbers represent the viscosity and quality of the oil. The viscosity is often indicated by SAE grades, where SAE stands for the Society of Automotive Engineers. The 'W' denotes 'winter,' and a smaller number before the W indicates better low-temperature fluidity of the oil, meaning it can be used in lower environmental temperatures and offers better engine protection during cold starts. The number after the W represents the oil's high-temperature resistance; a higher number indicates better protective performance under high temperatures. The primary functions of engine oil are to reduce friction and wear between moving parts, remove sludge and varnish from the engine, neutralize acids produced by fuel and lubricant oxidation, improve piston ring sealing, and cool the engine by carrying away heat from moving parts.