What does "W" in the oil specification signify?

The "W" in the oil specification stands for "Winter." This designation indicates that the oil has been formulated to perform well in colder temperatures. The number preceding the "W" represents the oil's viscosity at low temperatures, providing an understanding of how the oil will behave during winter conditions. For example, in a 5W-30 oil, the "5" signifies that the oil has a lower viscosity and retains its flow at lower temperatures, making it suitable for winter use.

This specification is important as it helps ensure that an engine starts smoothly and operates effectively even in cold weather situations, where oil can thicken and inhibit proper lubrication. The other options do not accurately reflect the meaning of the "W" in the context of multi-grade oils used in automotive applications.