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2020 Onyx
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I think putting too much emphasis on just one parameter may give misleading results. A healthy TBN doesn't mean the oil is good to go - although a bad TBN means something.

Presumably the staff at Blackstone have seen so many UOA's that they have a pretty good grasp of what to look for and recognize certain patterns - on the other hand if they're bored to death with eyes glazed over it might make sense to look for yourself and not just read their summary in case something stands out.

First oil shears down and can be diluted by fuel so viscosity decreases, then after a while the oil oxidizes and TBN becomes an issue, viscosity increases. Meanwhile abrasive soot solids are accumulating in the oil contributing to sludge and viscosity increase as well.

The Blackstone guys surely know much more than that, and if they say you can extend intervals it's not just some internet armchair speculation - they've reviewed all the important information and are making a reasoned judgement on your behalf. While I haven't re-reviewed all the old Gen 6 UOA's my recollection is that they aren't urging people to extend their intervals on the direct injection engines.
 
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Outback 2021 Premium 2.5L
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473 Posts
Discussion Starter · #22 ·
I don't disagree at all. But I need to understand the metric to give it a context. The discrepency was bugging me. And yup. I check the review extended use check box and they never comment on it. Could be cause it is a relatively fresh engine, or because it is a DI boxer and all those other related factors from what must be a very large data set come into play....
 
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