Understanding Oil Viscosity Oil viscosity refers to how easily oil flows at a specified temperature. Thinner oils flow more easily at low temperatures than heavier, thicker oils that have a more honey-like consistency. Thin is better for easier cold weather starting and reducing friction, while thick is better for maintaining film strength and oil pressure at high temperatures and loads. Oil viscosity is measured and given a number, which some people also refer to as the “weight” (thickness) of the oil. The lower the viscosity rating or weight, the thinner the oil. The higher the viscosity rating, the thicker the oil. Motor Oil Viscosity Ratings Viscosity ratings for commonly used motor oils typically range from O up to 50. • With multi-viscosity oils, a “W” after the number stands for “Winter” grade oil • The numeric value of the first number (example 5W-20) is a reference point to the lowest applicable temperature • The SAE grade is a reference point to the oil viscosity at operating temperatures SAE 20W-50 SAE 15W-50 SAE 10W-40 SAE 10W-30 SAE 5W-40 -30º -20º -10º 0º 10º 20º Fahrenheit SAE Viscosity Grade & Outdoor Temperature 30º 40º 50º 60º 70º 80º 90º 100º -34º -29º -23º -18º -12º -7º Celsius -1º 4º 10º 16º 21º 27º 32º 38º Technical Questions? Visit belray.com and contact our Technical Services department! TECHNICAL 2
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