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Society of Automotive Engineers

SAE rates engine oil viscosity. Viscosity is defined as the resistance to flow. Engine oil is available in single (e.g., SAE 30) and multigrade (e.g., SAE 5W-30) viscosity ratings. An oil that has two numbers in the rating is called a multigrade oil. Multigrade oils have been tested at various temperatures, and thus, can be used in a wide range of climates.The W after a rating signifies that the oil has been tested for a winter weather temperature at 0ºF (-18ºC). If there is not a W after the number the oil was tested at 210ºF (99ºC). The higher the viscosity number the thicker the oil. 5W-30 oil acts like SAE 5 when cold and SAE 30 when warm. It is thin enough when the engine is cold to get to all of the components and thick enough when the engine warms up to protect against engine wear. This is why multigrade oils have become so popular – they meet the viscosity ratings in multiple temperature ranges. Common engine oil viscosity ratings for newer vehicles are 0W-20, 5W-20, and 5W-30, but always check the owner’s manual for the manufacturer’s recommendations.