Originally Posted By: ExMachina
Originally Posted By: slacktide_bitog
The 0w implies better at cold temps than 5w. The difference may not be significant, but it certainly won't be worse.
I use Castrol Edge 0w30 in my older VQ30
It will be worse, but not by much. The "0w-" part just means what the oil does in cranking at -35 degC, and -40 degC pumpability limits, and the "5w-" cranking/pumping is done at warmer temperatures than "0w=". At a relatively warm 10 degF, the 0w-40 is thicker than a full-syn 5w-30 is. Its confusing, but the 0w-40 does this trick by using more PAO, and ostensibly, more PPD and VII, chemistry.
Yes, since 10F is only about -12C, we aren't down into the crossover point where the 0W-xx beings to thicken less than the 5W-xx lubricant, which is somewhere around -15C.
CCS and MRV can both be extrapolated backwards from their respective measuring points and halved at 5C increments. This is a "general" rule of thumb and works up to about -20C to -15C, somewhere in that neighbourhood. Just like the Viscosity Calculator doesn't work below 0C, extrapolating CCS and/or MRV backwards doesn't work at much above -15C IIRC.
Now, there are of course oils that, despite their 0w-xx designation, will still be thicker at their measuring points than a lighter grade in the next "winter" classification up. KrisZ and I were having a similar discussion a while back and he was able to find a 5w-30 that was actually thinner than the 0w-xx oil we were discussing at the time (which may have been M1 0w-40) going by the halving rule at the acceptable range of temperatures for the 5w-xx lubricant. It simply reached its gel point sooner, likely due to not having the same quantity of PAO.