The "15W" in 15W-40 engine oil stands for which of the following?

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The "15W" in 15W-40 engine oil indicates the oil's viscosity when measured at low temperatures, specifically at 0°F (-18°C). The "W" stands for "winter," signifying that this rating reflects the oil's performance in cold conditions. A lower number preceding the "W" indicates a thinner oil, which is essential for starting an engine in cold weather, as it flows more easily.

For instance, an oil rated as 15W will flow at lower temperatures, making it easier for the engine to crank over and circulate oil quickly during those cold starts. In contrast, the second part of the designation, "40," reflects the oil's viscosity at operating temperature (100°C), assuring that the oil maintains appropriate lubrication properties under normal engine operating conditions. Understanding these viscosity ratings helps in selecting the right oil for specific climate conditions and engine requirements.

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