Where did you read that? It's not even close to correct. You seem to be getting caught up in the Group III vs PAO/Ester thinking about the "quality" of base stocks. It's the viscosity modification additives that shear, not the base stock, and generally speaking 0w oils have more than 5w or 10w oils. Take Redline for example, all their oils are PAO/Ester, the 5w30 has no VIIs at all, while the 0w30 needs some to meet the 0w requirements. As a result, the HTHS, shear stability and temporary shear ratio of the 5w30 is substantially better than the 0w30.
Which German Castrol? The original "green" formula or the later "gold" one? The former was more shear stable than the latter. I saw 10%+ shear with GC in my WRX. UOA history is
here.
Are you referring to M1 formulations other than the ILSAC grades as well liked? M1 seems to design their ILSAC grades to shear on purpose, why they do this I haven't figured out, but most of their thicker grades are more shear stable today. The old 0w40 was not, however, often coming out of an engine thinner than supposedly thinner GC. The new API SN 0w40 is much more shear stable, and coincidentially made from Group III base stock where the old API SM formula was PAO.
M1 AFE 0w20 actually has quite poor shear stability, often shearing more than 15% in use. I know this from personal experience using it in my R18 powered Civic. The 5w20 is more shear stable. Strangely, AFE 0w30 is also more shear stable than AFE 0w20, at least that's my father's experience in his Subaru Outback 3.6. At least one user had good stability with AFE 0w30 in a Forester XT as well.
My latest UOA with AFE 0w20 is
here, with a link to prior thread in the first post. Another UOA for M1 AFE 0w20 in a Civic is
here, 6.8 cSt KV100!
And here you've hit on it, oil companies are not under any obligation to use their "best" ingredients in every oil, and there's always the bean-counter driven temptation to cut costs and make up for bad quality with good marketing. See Mobil 1 5w30 ILSAC GF-4 for an example. Unfortunately 0w requirements don't stop them from taking the low road. 0w oils have the most stringent requirements, but those requirements are irrelevant to the vast majority of users and can be met with "low quality" base stocks and a big dose of pour-point modifiers and viscosity index improvers. Not a good thing. In the end we simply have to evaluate each oil formulation individually, which means reading the PDS carefully, sifting the marketing speak through a giant BS filter, and filling in the gaps with UOA data. Hardly a perfect process, but its the best we've got.
PP 0w20 has a very good NOACK for a 0w20, but I wouldn't call it stellar at 10.8%. The prior formaula of Pennzoil Ultra 5w20 had a NOACK of 6%. Mobil 1 ESP 5w30 and Redline 5w30 are also in the 6% range.
Yea, but SubieNate is not exactly correct. If you were to formulate the cheapest 0w20 oil that would meet the minimum requirements and compared it to the cheapest 5w20 oil it would be hard to tell which was worse. Both would be bad, the least bad choice would depend on the engine and how it was used.
Luckily oil formulators have multiple product lines and the need to differentiate between those lines gives us some confidence in the quality of 5w and 10w grades. If SOPUS were truly cynical they'd re-package Pennzoil Conventional in bottles labeled "Platinum" and "Ultra" and market it at suitably inflated prices, but they're not
that cynical. Platinum really is better than PYB and Ultra is a slight step up from Platinum. Same goes for all the formulators.
A quick look at the PDS and UOAs bears this out, PU 10w30 is an excellent oil for high temperature use provided it's the right viscosity and extreme cold starts aren't on the menu.
1 - What's Mobil
e 1? I assume you mean Mobil 1.
2 - There's no such thing as non-synthetic Mobil 1. XOM's non-synthetic oil is called Mobil Super, formerly Mobil Clean 5000. I assume you're getting caught up in the Group III vs PAO/Ester nonsense. The general consensus is the ILSAC GF-4 formulation of Mobil 1 5w30 was substandard, but that's not due to the base stock, it's the additive package. Most ILSAC GF-4 5w30 oils turned into 5w20 in turbo Subarus, its just that M1 was the most common choice among those who didn't study the manual and see that thicker grades were required for high temperatures or heavy use. GF-5 oils are better, but still too thin for my comfort in a turbo EJ Subaru engine. That doesn't make them "bad" oils though, just mis-applied. A slightly thicker oil with the same additive package should be great in a turbo EJ, which is the theory I'm testing right now with Mobil 1 ESP formula 5w30 in my WRX.