Which engine oil covers the largest range of temperatures?

In German traffic and vehicle regulations, engine oils with "W" (winter) in their designation, like SAE 10 W 40, are multi-grade oils. They are designed to perform well over a wide range of temperatures, both cold and hot. The first number (10 W) indicates how the oil flows at low temperatures, ensuring better cold starts. The second number (40) indicates how the oil behaves at high temperatures, providing adequate lubrication when the engine is hot.

Single-grade oils like SAE 30 do not have this temperature adaptability; they are thicker at low temperatures and may not protect the engine well when cold. SAE 10 W 30 is also multi-grade but has a narrower high-temperature range compared to SAE 10 W 40.

Therefore, SAE 10 W 40 covers the largest temperature range among the options, making it suitable for different climates and varying engine conditions. This versatility is why it is often recommended.