TAN testing on VOA?

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dparm

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About to send in a VOA sample to Blackstone. Is it worthwhile to get TAN tested on unused oil in addition to TBN?

I understand the whole concept of TBN/TAN crossover, but I am unsure as to the value (if any) of knowing an oil's starting TAN.

Oil in question is RLI Bio-SynXtra 0w30.
 
As far as I understand it TAN is the acidity of the oil caused by breakdown, moisture and heat.
Someone else can probably explain it better, but I would say no.
 
I was under the assumption that certain basestocks (such as the esters in RLI) might have natural acidity and hence also have high TBN.
 
The TAN (Total Acid Number) is the amount of potassium hydroxide measured in milligrams needed to neutralize the acids in one gram of oil. When plotted on a graph with the TBN, the point at which the two lines cross is the optimal point to change your oil and indicates nearing additive depletion. For cost reasons I didn’t get the TAN test done because the TBN is a more reliable method to determine the active additive remaining.
References:

Stark, J. (n.d.). Spectrometry: The Marvel Of The Lab. Retrieved April 6, 2011, from Blackstone Labs: Link
What Is Oil Analysis? (n.d.). Retrieved April 6, 2011, from Bob Is The Oil Guy: Link
Sources Of Wear Metals In Oil Analysis. (n.d.). Retrieved April 6, 2011, from Bently Tribology Services: Link

Tags: Analysis, Engine Oil

http://www.bobistheoilguy.com/engine-oil-analysis/
 
Right, I understand that. But we're talking about a "virgin" (unused) oil sample here. I assumed that the TBN is most important in unused oil since it's indicative of the oil's reserve capacity to neutralize acids, but was thinking that certain oils might have a high starting TAN.
 
From that paper they are always breaking down at a very slow rate so yes there should be a little acid in them at any given time, it shouldn't add up to much but if your curious why not.

Just plain old H2O breaks down esters as well so a bottle with a broken seal will have more acid than a properly sealed bottle.
 
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I honestly wouldn't worry about it Esters will have higher acids always no matter what, the exact concentration in virgin oil should be trivial unless you unsealed the bottle and left for several days or weeks even in high humidity and shook it up remixing several times. I wouldn't worry about it at all to be honest.
 
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If the decrease in TBN and increase in TAN were linear, having both starting TBN and TAN (VOA) as well as used oil TBN and TAN, you could extrapolate to see how much longer you could run an oil before the two lines cross. Alas, we all know it's not linear, so from that standpoint, virgin TAN may not be of much use.

In addition, most labs will ignore TAN value in drawing UOA conclusions in gasoline engines. They seem to think it's more relevant in diesel applications. I know Wearcheck looks at both and will flag a UOA if your TAN reaches 80% of TBN. So, looking at my last PU UOA, TBN was 3.6 and TAN was 3.8. Wearcheck's recommendation was to change the oil. But if it was Blackstone, they would have said the oil is suitable for continued use. Who's right? I don't know.
 
I've sometimes wondered if getting virgin TAN and using that oil exclusively for a while might be beneficial. For instance, monitoring TAN/TBN relationship of the same oil used after various OCIs, etc, would that reveal anything about the inherent internal condition of an engine relative to cleanliness?

Perhaps it's more of a reflection on how quickly the TBN/basestock quality of the lube itself is at preventing harmful acidic numbers to creep. I think there may be something to the variable of TBN/TAN relationship and perhaps fuel used/maintenance habits and relative ocndition of the engine are part of the contributing factors.

For this reason, I can see why TBN alone is more important as a baseline. However, with TAN one may also see red flags or understand more so why TBN retention for instance may be poor in 1 app/engine but better in the 'same' app/engine that sees worse conditions/deposits etc and has a dirtier engine to begin with.
 
For the first time I told Blackstone to give me the TAN in my used oil. I am curious how my driving habits contribute to acid buildup.


My car sits for 5 or more days in a climate controlled garage without being driven. There have been periods where I haven't driven it for two or three weeks. When I do, it's often in very slow traffic in downtown Chicago. I make the effort to get it on the highway sometimes. And yes, I do run the V8 powerplant pretty hard. :-)
 
Originally Posted By: dparm
My car sits for 5 or more days in a climate controlled garage without being driven. There have been periods where I haven't driven it for two or three weeks. When I do, it's often in very slow traffic in downtown Chicago.

Have you seen my last UOA with TBN and TAN? My driving patterns have been very similar to yours. The car sits during the week and gets driven around town once or twice during the weekend.
 
Originally Posted By: dparm
Thanks. Your TAN-TBN ratio isn't looking very good...

I know. That's why I agreed with Wearcheck's suggestion and went ahead and changed the oil. Although, looking at wear metals, I can't really see any ill effects. Also, this was my first fill with PU. From what I've read, the first time you run a particular oil, it tends to deplete faster, so subsequent runs may show better TBN retention and slower TAN uptakes.
 
Capa, yes, although his experience was mainly related to diesel engines where I believe monitoring for TAN has more applicability. Alas, I already forgot why that was.... uhh.
 
^Isn't it because soot formation in a diesel will creep to high before TBN is ever depleted to be relative to changing the oil? Or is it something along the lines of 'similar' contributing factors raising TAN before TBN is completely depleted, etc?

So, then the opposite is more applicable to non-diesel apps. At least non-HD.

TAN rates won't get too high before TBN depletion is far enough to condemn the 'oil'...BUT what does that say definitively about the 'left over' condition of the engine? The lube might be alright. However, for example is it a guess at how much deposit formation was left over or not in the engine itself that is still on the bare metal surfaces or at the bottom of the oil pan, etc.
 
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