Consequently, if the motor oil performs like a SAE 20 motor oil at the reduced temperatures (the scale varies - see the chart), then it will be a SAE 20W motor oil. If it performs like a SAE 0 motor oil at the colder temperature, then it will receive the SAE 0W viscosity grade. Basically, as shown by the chart, when the oil is reduced to a colder temperature it is measured for performance factors. Now if you look at the table labeled Winter or "W" Grades, you can get valuable information on how the W or winter grade viscosities are measured. Consequently, if a motor oil flows through faster than 9.3 and slower than 12.5 seconds, then it will be a SAE 30 viscosity. If you look at the table, SAE Viscosity Chart (High Temp) you'll see that if a measured amount of motor oil flows through the viscometer at 210° F (100° C) faster than 5.6 but less than 9.3 seconds, then it will be considered a SAE 20 viscosity. There is a scale for the W, or winter viscosity grades and, depending on which grade is selected, testing is done at different temperatures. Simply put, these tests are done with a different temperature system. Less dry running means much less engine wear. The quicker the oil flows cold, the less dry running. The advantages of a low W viscosity number is obvious. This allows the engine to get quick oil flow when it is started cold verses dry running until lubricant either warms up sufficiently or is finally forced through the engine oil system. For example, a 5W-30 motor oil performs like a SAE 5 motor oil would perform at the cold temperature specified, but still has the SAE 30 viscosity at 210° F (100° C) which is engine operating temperature. The difference is when the viscosity is tested at a much colder temperature. In other words, a SAE 30 motor oil is the same viscosity as a 10w-30 or 5W-30 at 210° (100° C). The numbers without the W are all tested at 210° F or 100° C which is considered an approximation of engine operating temperature. What does a 5W-30 do that an SAE 30 won't? When you see a W on a viscosity rating it means that this oil viscosity has been tested at a Colder temperature. These are translated into the easier to understand SAE viscosity numbers you see on an oil bottle. You will see oil viscosity measurement in lube articles stated in kinematic (kv) and absolute (cSt) terms. The thicker (higher viscosity) of an oil, the slower it will flow. Simply put, viscosity is the oil's resistance to flow or, for the layman, an oil's speed of flow as measured through a device known as a viscometer. This leaves them still wondering what the viscosity numbers really mean on a bottle of motor oil. really? Most of the time when viscosity is explained words are used that are too technical for the average person to quickly grasp. What does the SAE Viscosity rating on your Motoroil bottle mean? How do they come up with this rating.
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