Lubricants — Which organization defines engine oil viscosity grades? Engine oil viscosity grades such as 5W-30 or 15W-40 are established by which standards body?

Introduction / Context:
Viscosity grade numbers on engine oils (e.g., 0W-20, 10W-40) indicate flow characteristics at cold and hot temperatures. These grades are standardized for consistency across brands and markets.

Given Data / Assumptions:

• Multigrade engine oils for passenger and commercial vehicles.
• Common retail labels and owner’s manual references.

Concept / Approach:
The Society of Automotive Engineers (SAE) defines the J300 viscosity classification specifying kinematic and cranking viscosity ranges at various temperatures. The American Petroleum Institute (API) defines performance categories (e.g., SP, CK-4), not the viscosity numbers themselves. ATF and GVW are unrelated to viscosity grading; ISO viscosity numbers apply mostly to industrial lubricants, not automotive engine oils.

Step-by-Step Solution:
Identify the standard for viscosity grades → SAE J300.Recognize API's role → service categories and performance, not the grade numbers.Select the organization: SAE.

Verification / Alternative check:
Owner's manuals list recommended SAE grades; oil product data sheets cite compliance with SAE J300.

Why Other Options Are Wrong:
ATF/GVW: not standards bodies or relevant specifications for engine oil viscosity.API: performance/service classification, not viscosity grade definitions.ISO: industrial oils mainly, different numbering scheme.

Common Pitfalls:
Confusing API SP/CK-4 with SAE grade; both appear on oil labels but indicate different attributes.

Final Answer:
society of automotive engineers (SAE)