What is the temperature range for 10W 40 engine oil?

10W-40 engine oil is formulated for use in temperatures ranging from -22°F (-30°C) to 104°F (40°C). The "10W" part of the name refers to the oil's viscosity at 0°F (-18°C), while the "40" refers to its viscosity at 212°F (100°C). The lower the first number, the thinner the oil is at low temperatures, making it easier to start your engine in cold weather. The higher the second number, the thicker the oil is at high temperatures, which helps to protect your engine from wear and tear.