Monograde oils, such as SAE 30, are designed for stable, consistent temperatures, providing excellent lubrication. However, they are not ideal for fluctuating temperatures. In contrast, multigrade oils like 10W-40 (''W'' stands for ''Winter'') perform well across a wide range of temperatures, offering better cold-start performance and stable lubrication at higher operating temperatures. Multigrade oils are generally preferred for modern vehicles, while monograde oils may be better suited for specific applications with consistent conditions, such as certain industrial machines or high-temperature environments.