There are different viscosity grades for an approval. Besides, if you were satisfied with the approval stamps and didn't care about brand and viscosity choices, you wouldn't be reading this forum.
That's not how oil formulation works. They use the same VII across the viscosity grades, as the type of VII is dictated by the engine-deposits requirements of a given approval. Your statement should be corrected as "0W-40 is formulated using
thinner base stocks (a
thinner base oil) and
more VII." I already explained the reason for this in this thread, and you can read the explanation (basically added VII increases the MRV so that the base-oil viscosity must be reduced to compensate for that). See my table for the VII content and base-oil viscosity to see how different oils compare. Again, a 0W-40 will typically be thinner and result in more wear than a C3 5W-30 using the same additive package. A 5W-40 should be thicker than both and result in least wear. If you are starting the car on the Alps, sure, use 0W-40. You may see a slightly better base oil with 0W-40 than a 5W-40 for a given approval. My favorite Euro viscosity grade is C3 5W-30, as it has an HTHS the same as that of a 0W-40, a thicker base oil, and a lot less VII. It will also experience less permanent shear due to lower VII content and will have a higher HTHS with used oil. I don't know why Porsche insists on C40 as opposed to C30, as the HTHS and base-oil viscosities are not higher for a C40 than for a C30. Old habits die hard. Classic models require xW-50 and xW-60, which makes sense.
www.porsche.com
But they aren't formulated the same. The above assumes that they won't swap out cheaper base oils with the narrower spread, but that's exactly what they do. Look at these the below 5w-40 Euro example blended with PAO and AN:
Now, let's compare to these Group III examples:
MUCH higher VII content.
In fact, if we then compare to a few different 0w-40's:
1. Group III + PAO, low BOV, but VII load is actually lower than the above Yubase examples:
2. PAO/AN based. BOV balances to about the same as our Group III 5w-40's, VII load about the same:
3. PAO/Ester based, BOV is actually higher than the Group III 5w-40's, VII load is lower:
In all instances except the Yubase + PAO blend, the two base oil viscosities used are the same in the 0w-40 and our Group III 5w-40.
So, if the 5w-40's were being blended with straight or mostly PAO, like Mobil shows in the last two tables, yes, the BOV of the base oil blend would be higher and VII load lower, but we know that typical 5w-40's aren't blended that way. If we look at Castrol for example, their 5w-40 is straight Group III, while their 0w-40 is predominantly PAO-based.
This is the chasm between idealized blending philosophy and large, capitalist oil companies using the cheapest bases they can get away with while meeting the performance targets. If you go Unicorn shopping and buy something like Ravenol 5w-40, it should be blended more similar to the last table, but what you buy from Mobil, Shell, Valvoline or Castrol is going to be heavy on the Group III.
The wildcard seems to be the constant shuffling of the bases used in M1 FS 0w-40. Recently being 50-60% Group III with 10-20% PAO, similar to Formula M 5w-40, which is also 50-60% Group III (but they don't list the remaining base, so who knows what that is (could be EHC)), now 30-40% PAO.
In fact Mobil shows that you can get away with a good slug of 5cSt Group II+ in a 5w-40:
And even a bit more EHC 5cSt in a C3 5w-30:
It comes down more PAO in the base oil blend is going to mean less VII, you can't just go by the spread, because you may end up with the same VII content due to the bases selected to make the product blending more cost effective.
