What does the marking SAE 10W-30 on a bottle of engine oil indicate?

• A. Type of oil derived from natural resources
• B. Viscosity of the oil at cold temperature and at 100 °C
• C. Amount of additives in the oil
• D. Color of the oil

Answer: (B)

The marking SAE 10W-30 on a bottle of engine oil indicates the viscosity characteristics of the oil, specifically how it performs at varying temperatures. The "10W" signifies the oil's viscosity at cold temperatures. The "W" stands for winter, meaning that it will flow at temperatures as low as those expected during winter conditions. A lower number, such as 10, suggests that the oil remains fluid and can protect the engine at these colder temperatures.

The "30" indicates the oil's viscosity at 100 °C (or the operating temperature of a typical engine). Oils with a higher number in this position will maintain their viscosity and provide a stable film of lubrication at the engine's operating temperature, which is essential for reducing wear and tear on the engine components during normal operation.

This dual-rating system allows consumers to choose an oil that provides effective protection across a range of temperature conditions. Therefore, this marking is crucial for ensuring that the engine oil will perform effectively under both cold starts and normal operating conditions.