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I may be missing something but I'm guessing that the viscosity measuring methodology is different for cold oil versus hot oil? If the 30 in 10W-30 means 30 seconds, then what does the 10 represent; 10 minutes???
Quote from: Rubberhead on September 25, 2014, 04:29:10 PMI may be missing something but I'm guessing that the viscosity measuring methodology is different for cold oil versus hot oil? If the 30 in 10W-30 means 30 seconds, then what does the 10 represent; 10 minutes???10W-30. the 10 is the viscosity rating on cold weather, and the 30 for warm. The "W" is for winter.
Quote from: oldskool49 on September 25, 2014, 08:50:01 PMQuote from: Rubberhead on September 25, 2014, 04:29:10 PMI may be missing something but I'm guessing that the viscosity measuring methodology is different for cold oil versus hot oil? If the 30 in 10W-30 means 30 seconds, then what does the 10 represent; 10 minutes???10W-30. the 10 is the viscosity rating on cold weather, and the 30 for warm. The "W" is for winter.Right, I get that but what does the 10 represent; seconds, minutes, hours or something else entirely. If 30 is 30 seconds for warm oil, then you would think that the number for winter oil would be higher since the colder oil would be thicker and would flow slower. I'm just trying to understand the disparity between the numbers.
When you see a W on a viscosity rating it means that this oil viscosity has been tested at a Colder temperature. The numbers without the W are all tested at 210° F or 100° C which is considered an approximation of engine operating 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 difference is when the viscosity is tested at a much colder temperature. 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. 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. The advantages of a low W viscosity number is obvious. The quicker the oil flows cold, the less dry running. Less dry running means much less engine wear.