Originally Posted By: JHZR2
And rarely is TAN and TBN given from what ive seen.
I like the concept of 2+ TBN. This is really arbitrary, but I like the concept of there being a quantity of active additive in there buffering. The reality is that the closer you get to the equivalence point (think titrations in HS chemistry, where your fluid changed color), as you get to the equivalence point, the reaction effectively slows because of mass transport limitations, and so there is more active time with acid content in the fluid.
^Exactly, if the starting TAN is increased more than 4, whilst the TBN starting number goes down more than the stated 65% of starting number, I'd say that's a good point for any oil in an extended service application to be 'considered' as ready to change at the next convenient time. Even if you truly had a buffer of say, 2,000 miles after that point before exposing the engine to less than ideal conditions.
For instance, 65% of the stated 12.6 TBN of Amsoil's signature lineup would mean to start looking to change the oil after the TBN reaches 4.4...I'd say 75% of original TBN depletion is a good threshold for such a high quality oil...in other words; anywhere between 2-3 TBN remaining would be optimum for THAT oil, IMO. That gives me peace of mind and I feel like I've gotten a good value for my interval.
Now, also relative to this if the starting TAN of AZO(0w30 Amsoil) is 3.6 or so according to Artem's VOA posted here:
https://bobistheoilguy.com/forums/threads/amsoil-azo-0w30-with-tan-and-tbn-blackstone-labs.154343/
If the TAN rises to double that, or 7+...I'd say it's time to change the oil...and I'd expect the TBN to be down around 3 by then anyway.
So, for that particular oil that's my 'current' feel for things in my app. Your MMV, or your opinion, but for another oil perhaps the depletion of 65%(0.65) is more applicable. Say, for a petroleum based conventional. A TBN starting of 8 on a conventional PCMO, would then have a TBN of about 2.8 or so...not far from where most would change it(by about 2.0 'most' would say).
I think there are 'general' guidelines, but insols/particle counts/wear ppm(AFTER establishing a trend for YOUR engine in normal 4-5k mile OCIs, for instance), is also extremely important in determining how long an oil should remain in even if TBN is strong. If enough contaminants are present why risk 'elevated' wear by extending out the oil change intervals too long, at least prematurely? That is what I'm running into with my VX.
The insols are high in my app, I haven't gotten a particle count(PC) yet, but even the best oil filter won't grab a ton of gunk if an engine is in need of any form of 'cleansing'(that is, varnish and carbon deposits at a minimum, not necessarily 'sludge')...to top it all off I'm not sure I'll keep the K&N even if I think it's not allowing in 'excessive' amounts of Si just because if any 'did' ever get in more so because of 'less' filtration ability compared to a quality OE paper...I'd be concerned about any elevated wear prior to the drain and potentially another interval with elevated Si as a result.
I'd say anything over 3 ppm/1,000 miles of actual dirt entry in an extended app(10,000+) is probably a good 'goal', but more realistically any rate over 5 ppm/1k is starting to get into a 'dangerous' amount of Si for overall engine life expectancy.
Okay, so that's how I feel in general for extended OCIs, related to TBN as well. Perhaps I'm off base, but it's the gist of what I've gathered in my relatively short time here.
