How does engine oil viscosity rating like 10W-30 reflect temperature performance?

How does engine oil viscosity rating like 10W-30 reflect temperature performance?

• A. The first number indicates high-temperature viscosity; the second indicates cold-start viscosity
• B. The first number indicates cold-start viscosity; the second indicates high-temperature viscosity
• C. The numbers indicate engine RPM range
• D. The numbers indicate oil color

Answer: (B)

Engine oil viscosity ratings like 10W-30 show how the oil behaves across temperatures. The first number, before the W, is about cold-start viscosity: a lower value means the oil is thinner when it’s cold, helping the engine start and crank more easily in cooler conditions. The second number, after the dash, is about high-temperature viscosity: it indicates how thick the oil remains when the engine is hot, providing a protective, lubricating film at operating temperatures. So the first number represents cold-start viscosity and the second represents high-temperature viscosity. The other options don’t describe how viscosity ratings relate to temperature performance.

Engine oil viscosity ratings like 10W-30 show how the oil behaves across temperatures. The first number, before the W, is about cold-start viscosity: a lower value means the oil is thinner when it’s cold, helping the engine start and crank more easily in cooler conditions. The second number, after the dash, is about high-temperature viscosity: it indicates how thick the oil remains when the engine is hot, providing a protective, lubricating film at operating temperatures. So the first number represents cold-start viscosity and the second represents high-temperature viscosity. The other options don’t describe how viscosity ratings relate to temperature performance.