Question: what is the difference between motor oil weights?
Answer: The "W" stands for winter, not weight as many people think. The lower the number here, the less it thickens in the cold. So 5W-30 viscosity engine oil thickens less in the cold than a 10W-30, but more than a 0W-30. ... For example, 10W-30 oil will thin out at higher temperatures faster than 10W-40 will.