Engine Oil
3 indexed entriesPart of Automotive & Vehicles.
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API Service Categories
API service categories rate gasoline engine oil performance and are updated periodically by the American Petroleum Institute. The current category is API SQ, introduced in March 2025 alongside ILSAC GF-7, superseding API SP (May 2020), which replaced API SN (October 2010) and its LSPI-focused interim update, API SN PLUS (May 2018).
Brake Fluid Types
US DOT brake fluid grades differ mainly in boiling point and chemistry. DOT 3 and DOT 4 are glycol-based and absorb moisture over time; DOT 5 is silicone-based, water-repellent, and must never be mixed with the others; DOT 5.1 is glycol-based with a boiling point matching DOT 5. Higher boiling points resist brake fade better.
Engine Oil Viscosity Grades
SAE J300 classifies engine oil viscosity with a two-number code like 5W-30: the number before 'W' rates cold-flow performance in winter, while the second number rates viscosity at 100 degrees Celsius operating temperature. Lower winter numbers mean better cold starts; higher second numbers mean thicker oil when hot.