What is the oil viscosity grade specified?

• A. 5w20
• B. 10w30
• C. 20w50
• D. 15w40

Answer: (B)

Oil viscosity grades tell you how thick the oil is at cold start and when the engine is hot. In a multi-grade oil, the first number before the W measures how the oil flows in cold conditions (the lower this number, the better the oil protection during a cold start). The second number after the W shows how thick the oil remains at operating temperature (the higher this number, the thicker the oil at hot engine temperature).

Choosing 10w30 as the specification means the oil is formulated to flow well when starting a cold engine but still provide enough film strength to protect moving parts once the engine is hot. It’s a common, middle-ground choice that works well across a broad range of climates and engine designs, offering a balance between easy cold starts and solid high-temperature lubrication.

The other options represent different needs: 5w20 is thinner at both cold and hot temperatures, which might not provide sufficient protection in some engines or conditions; 20w50 is much thicker at operating temperature, which can reduce efficiency and flow in normal summer conditions; 15w40 is often used in diesel engines or older gasoline engines and may be too viscous for many modern engines in milder climates. For many standard engines, the specified grade is 10w30 because it provides reliable protection across a wide range of temperatures.