Originally Posted by Char Baby
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If this helps...
Mobil 1 is more shear stable. And M1 is also a bit more robust to start with in its KV @ 40c/100c degrees so, it'll maintain its stability longer as well as being a full synthetic while the M-D/M makes no claim of being anything other than conventional fluid(not even a blend).
I thought it odd that the conventional fluid would have a higher VI than the same manufacturers synthetic product. I suppose since the base oil VI of Mobil 1 ATF is acceptable without VI index improver additives, they at fine with that VI. The conventional product requires VI improvers, so the resulting fluid ends up with a higher VI than the synthetic, but at the cost of shearing potential. There must be a reason they don't use less VI improvers in the conventional fluid, even though it logically appears that this fluid would end up more shear stable, maybe it isn't so.
Dex III has a reputation for shearing, leading many to recommend Dex VI, which is thinner, but more shear stable. It seems that manufacturers have designed and continue to make a product using additives that predictably will shear, possibly out of grade. To this layman, it seems a better course would be less VI improver and a lower as blended VI. It does look good on the data sheet, which could be attractive to buyers, but very few customers know what VI is and ever see a data sheet.
