Originally Posted By: XS650
Originally Posted By: Bob_B
I've often wondered how a company can rate its oil as "0W". Per the usual definition of the oil's viscosity, the first number is derived from the amount of time, in seconds, that the oil takes to run through a controlled measuring device at a standard low temperature. Nothing can run through in 0 seconds, so where do the manufacturers get this number?
0w comes from SAE J300. SAE viscosity ratings such as 0W, 5W, etc are not actual viscosity numbers. They mean that the oil is within a range of viscosity that is spelled out in SAE J300. The actual units of viscosity used in J300 are centiStokes (cSt).
The two xW tests are done at two different low temperature for each xW rating and neither test is done by timing the oil through a simple measuring device like in the olden daze.
There are several ways to measure oil viscosity, timing it through a measuring device isn't the only way.
XS650, perfect answer. Accurate, simple, helpful. If only all questions were answered in such a manner.