That 2% figure is in terms of the percentage of VII content in the entire formulated oil. A 0w30 may have around 50% more VII than a 5w30 (~4% vs 6% VII content).
BITOG member Ghokan published a good spreadsheet that shows VII content and full shear viscosity (HTFS) estimates of various oils. Taking an example, Mobil 1 5w30 has 4.4% VII and an HTFS of 2.32 cP, while Mobil 1 0w30 has around 6.9% VII and an HTFS of 2.02 cP. In full shear conditions, the 0w30 has a viscosity somewhere in between that of a typical 0W-20 and a 5W-20, so it's about a full grade thinner in high shear conditions.
Remember, Gokhan's estimates were just that, estimates, and there were many oils that clearly didn't function with the estimation function, yielding wildly off-side results.
Here's a 5w30 with 8.5% VM:
Here's one with 11.74% VM:
The 0w30 in this table has 7% VM, the 5w30 2.8%, when both are blended with PAO, but then so were the previous examples:
Here's a 0w30 with 5.7% VM:
Two Group III-based 5w30's, 9.1% and 8% VM:
The examples are myriad. It's not safe to simply assume that the 5w30 has less VM.
As we've seen with Mobil, they use different slates of base oils for the different grades, they are not doing those SpectraSyn PAO examples, because they can, and do, use cheaper base oils in the grades that aren't shooting for the 0W-xx Winter grade.
twX said:
The puming viscosity will be lower as well. The thinner oil will have a higher flow rate to the engine when the oil pump is bypassing, and the oil pump on any engine will be bypassing on any cold start in winter conditions.
What temperature are you considering winter conditions? Because both my vehicles don't always go on the relief during the winter months. Yes, my Jeep does when it gets down around -15C or lower, but we do not see those temperatures consistently all winter.