Engine oil ratings, which are produced by the Society of Automotive Engineers, or SAE, classify oils on a numerical system to help consumers find the oils that work best for their cars based on year and winter rating. Oils are rated on a numerical scale in increments between 0 and 30. Oils have a special code that shows viscosity; the first number, which is followed by the letter W, indicates winter rating, while the second numeral shows high temperature rating.
The first numbers, which range between 0 and 25, indicate how well oils flow in colder weather. An oil with a rating of 5 is more viscous than one rated as a 10; the latter is ideal for cars in colder climates. The next number follows the same scale, and shows how well oils perform in warm temperatures. The highest rating is 30, which indicates oils protect engines even in hot weather.
Oil ratings appear in a star or donut-shaped seal, which indicates certification from the American Petroleum Institute. The top part of the seal shows the type of engine oils are suited for, using a 2 for gasoline engines and a 4 for diesel engines, along with performance. The bottom portion of the seal shows special attributes, such as energy-saving capacities and resource conservation.