Most modern motor oils are formulated from various grades of oil so the oil will have the best characteristics of both thick and thin viscosity oils. Straight SAE 30 oil is often specified for small air-cooled engines in lawnmowers, garden tractors, portable generators and gas-powered chain saws. Single weight oils are no longer used in late model automotive engines, but may be required for use in some vintage and antique engines. These may be multi-grade oils or single weight oils such as SAE 30, 40 or 50. Higher viscosity motor oils that are thicker and better suited for high temperature operation. There are also "15W" and "20W" grade multi-weight motor oils. Low viscosity motor oils that pour easily at low temperatures typically have a "0W", "5W" or "10W" rating. The oil weight is its viscosity index at 100 degrees C (the boiling point of water). The rating is determined in a lab using a cold crank simulator and mini-rotary viscometer test. The numeric value of the first number (example 5W-20) is a measure of the pour point of the oil expressed in degrees Celsius whent he oil is cold. With multi-viscosity oils, a "W" after the number stands for "Winter" grade oil. Viscosity ratings for commonly used motor oils typically range from 0 up to 50.
The higher the viscosity rating, the thicker the oil. The lower the viscosity rating or weight, the thinner the oil.
The viscosity of the oil is measured and given a number, which some people also refer to as the "weight" (thickness) of the oil. The viscosity rating of a motor oil is determined in a laboratory by a Society of Automotive Engineers (SAE) test procedure. Thin is good for easier cold weather starting and reducing friction, while thick is better for maintaining film strength and oil pressure at high temperatures and loads. Thinner oils have a water-like consistency and pour more easily at low temperatures than heavier, thicker oils that have a more honey-like consistency. Oil viscosity refers to how easily oil pours at a specified temperature. What You Should Know About Motor Oil Viscosity by Larry Carley copyright What You Should Know About Motor Oil ViscosityĪuto Repair Library, Auto Parts, Accessories, Tools, Manuals & Books, Car BLOG, Links, Index
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