As for myself, I might get my hands on a 4 or 5 qt jug of oil, though I need to fill a 5.6 qt case. Yes I could by another qt or 2, but what about those sitting I already have. As said, sometimes it's about saving a buck or two.
Having used synthetic for a few years on a new-to-me used car with no oil history, one especially cold winter left me with some leaking seals. Going back to mineral stocks seemed to slow things, and the current fill of HM mineral has it all but stopped. I've done a bit of work on vehicles like many of those around here, even an engine rebuild and customization during my school years. The battle against rust was however a wearing factor on my nerves having to deal with the salts and dirt that inevitably becomes airborn, damaging paint and glass alike. That said, I resist getting the engine hoist out of the shed and pulling the motor and FWD tranny. I could just pay a shop, but that would cost $800-1000 for just the rear main seal as I have heard from others on another forum. I'd personally go about replacing all the seals as at one point in the above situation, they just about all showed some leakage.
A poster on another topic had provided a link to VW and something to do with recommended oils/OCI's for their vehicle(s). It did mention that if one didn't have spec'ed oil but one of applicable viscosity, that up to a qt or so could be added to the crankcase for replenishment/top-off. The only thing I think they said in such case that could be viewed as negative, was something like reducing the OCI, say using the servere service OCI even thought one's operating habits may not fit such a category. In such a case, having the correct amount of oil is better than no oil - being that it's acceptible oil to begin with that is able to be used in such a category (gasoline engine, deisel engine, etc.).
There are situations like that above where one oil type has a less favorable side effect but is thought ideal for all operating extremes, but a lesser in comparison though still able in less extreme situations is used. One might think to tweak the viscosity characteristics for say cold weather start-up, by switching out a qt or two of mineral for synthetic, possibly of lower viscosity. Infrequant use and cold soak issues to contend with that has some effect on mineral bases initial flow performance isn't the case with synthetic's so I've come to understand, and the ratio of synthetic to mineral doesn't seem to upset seal issues so as to aggrivate leaks. Does it really provide any benefit? I honestly don't know for I'm not running side to side comparisons. Does it feel like I'm "helping" the situations? It does, but then when have "feelings" proved to be the deciding factor in all successes? - I think it something that's easiest to live with, having it been said that human's are emotional beings.
And then again, Some might just wish to see what happens, playing a dare or just chance...though in reality they could stand to lose out and find their pleasurable was are/were actually self defeating - that of course if they are actually paying close attention and are open to the truth of the matter.
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"We come into life, learning about life. Just what one does with such knowledge and experience is up to the individual and their abilities, resources considered."