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I am going to call this the impatient mode of application.
Surely so. There may be some situations where you're going to need to remedy the situation in a shorter time span. These can vary from consumer preference to the severity of the situation to be corrected. The difficulty I see for Frank is articulating for the customer WHEN such action would be appropriate ..or rather inappropriate.
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But remember that ARX is not indexed like the host oil. With two bottles loaded into the crankcase, low temperature viscocity of the mix is going to be high. And at full operating temperature its going to make the overall lower than spec for the oil to some degree. Cold weather pour point and pumpability may well be an issue with dino oil in the northern parts of the country, with 2 bottles loaded.
This part may be true, but I would offer that our engines are well buffered for insult that may arise from viscosity variances to a great extent. Most 5w-30 of the vintage of an advanced sludge engine would probably have sheared to 20 weights in service (some may still shear in some engines) and there are plenty of people who use heavier oils in colder climates and their engines don't evidence issues that are in excess of the other operational variables present. Not to discount your concerns/cautions, but one must, just like in any medical practice using modalities of treatment that have side effects, weigh the benefits against the potential risks. The condition that is being corrected has the engine at risk too (potentially). As much as we've gravitated toward thinner oils, you've got to realize that, in all but the most severe climates, heavier oils were acceptable year round if you recall some of the older owners manual recommendations. My own 4.0 in an older evolution spec'd 20w-50 down to (IIRC) 32F and never spec'd 5w-20. Yet the same engine survives fine on 5w-20 or 15w-40 in a climate that spans from single digits to 95F on either. Although not preferred, nor recommended, I would think that most engines are just as tolerant and that the side effects are more in terms of fuel economy. Just look at OZ and see how they're just now losing their grip on the 20w-70 oil and you can actually buy 5w-20 if you look hard enough.
Again, I think that articulating the sensible use is the hardest part of the two bottle treatment. We've got decent UOA data on the 100C effects of two bottles ..but I haven't seen much in terms of, for example, taking a 5w-30 dino and seeing how the VI is skewed with 2oz. added to it.