Originally Posted By: Gokhan
Well, none of the claims by Toyota are justified because all GF-5 oils satisfy the claims made by Toyota, not only the 0W-20 grade.
well, it's a marketing claim... that said, a thinner oil at startup is going in increase FE, and not all GF-5 oils will be the same in that regard, they all just have to meet a minimum standard. You're right though, some 5W20's may beat some 0W20's--you have to look at more than just weight. Still, a low COF 0W20 offers the best opportunity for highest efficiency.
Originally Posted By: Gokhan
There is really no cold-start benefit either unless you live in extremely cold climates (Canada, Alaska, etc.), as the cold viscosity is not that different from 5W-20.
Again, "it depends". Toyota's 0W20 is significantly thinner at start-up than many 5W20's, like 20% (or more) thinner at 100F. M1's 0W20, OTOH, isn't that thin until it gets really, really cold. So it's probably best to avoid blanket statements.
Originally Posted By: Gokhan
Regarding 10,000-mile OCIs and longer, I think you should use an oil with high initial TBN as well as good Mg content for TBN retention if you choose to go that way.
There are different ways to skin a cat. You seem to be dismissing the base oils being used and just focusing on the additive packs. Amsoil has consistently been a great performer for extended drains, and they use very little Mg in their formulations. Fuchs 507 oil is probably one of the best extended drain oils available, with almost no Mg. Maybe it's just cheaper to make an extended drain oil with a bunch of Mg?
Originally Posted By: Gokhan
Chances are that TBN will be OK for 10,000 miles without Mg, but then whenever it gets below 3.0, you should start to worry, as it may start increasing wear. Blackstone guys will say TBN is OK if it's over 1.0, but I think 3.0 is about the lowest you should go for better wear protection.
I haven't seen much, if any evidence to support that idea. I'm using an oil with a starting TBN of 5.2-6.2 (depending on who's measuring). Given the non-linear drop in TBN, based on your logic I should probably be doing 2K OCI's! Again, I don't think there's a "one size fits all" approach which really works with respect to TBN.