Originally Posted By: OVERKILL
The 0w-xx performance designation has no floor, only a ceiling for viscosity. Ergo, an oil could massively eclipse the CCS and MRV requirements and it would still handily fit under the 0w-xx designation.
As a practical point, given that the test temperature for MRV is -40C, a temperature not observed in most populous areas, pursuing a performance metric that divides the 0W-xx designation into a category lower at -45C wouldn't make a lot of sense.
Yep, this. Also, in colder areas that do see close to those temps have block heaters and other ways of keeping the oil at a temp that it will flow. No need for thinner.