TAN and TBN and further use?

[irv]

Dnewton3, and others, I am wondering if you can clear something up for me with regards to TBN and TAN?

I have read from a few here that without a TAN number, the TBN is practically worthless? Is this correct?

Also, with regards to TAN and if the TAN number is given, should an oil be discontinued for further use if it is getting close to the TBN number, or about to cross over the TBN number or already has?

I have seen the odd UOA where the TAN has crossed over the TBN number yet the analysis place has mentioned the oil is/was still good for further use and to increase the mileage on the next OC.

Color me confused, but IMO, based on my limited knowledge, I'd also say the oil should be changed if the TAN is about to cross and especially if it already has, but I honestly don't really know the answer?

Apologies if this has already been discussed, ad nauseum, but I have never seen it if it has.

 

[OVERKILL]

Keep in mind some oils have naturally high virgin TAN numbers, just like some have naturally high oxidation numbers (due to base oil selection) so while the TBN/TAN crossover "rule of thumb" is worth noting, it isn't always applicable or even advisable. Equipment manufacturer specifications on this is also important and they will have their own condemnation limits for TBN, TAN and many other parameters.

This article from a guy that works at Petronas supports this:
https://www.linkedin.com/pulse/gas-engine-oil-analysis-what-does-tantbn-crossover-beling-morales

 

[irv]

Originally Posted By: OVERKILL
Keep in mind some oils have naturally high virgin TAN numbers, just like some have naturally high oxidation numbers (due to base oil selection) so while the TBN/TAN crossover "rule of thumb" is worth noting, it isn't always applicable or even advisable. Equipment manufacturer specifications on this is also important and they will have their own condemnation limits for TBN, TAN and many other parameters.

This article from a guy that works at Petronas supports this:
https://www.linkedin.com/pulse/gas-engine-oil-analysis-what-does-tantbn-crossover-beling-morales


So basically one needs to know what the manu thinks, not what the UOA reads?

Personally, I think that would be next to impossible to find out because of the amount of different oils/brands that are in use today.

Am I wrong thinking that TAN should always be asked for if you are interested in the TBN number? Like someone said, not all TBN is the same and just because the TBN shows as still high or good, doesn't necessarily mean it is doing a good job at removing acids.

 

[Artem]

From my years and years of research in trying to understand your original question, I'd say that the TBN / TAN crossover condemnation point is probably accurate from a scientific oil analysis standpoint of the lubricant but over the years companies noted that although TAN is higher then TBN the oil is still able to do its job up to a point and can TECHNICALLY be used further without severe consequences... at least in the short term (during the typical warranty period).

Also engine design is a major player here. If an engine runs hot naturally and has hot spots inside the engine, then the high TAN and low TBN service interval will result in carbon / sludge build up because the reality is... the oil can't handle the build up chemically.

Now in the same scenario in an efficient, well designed engine, no problems will show up because the highly acidic oil isn't being baked into the pores of the engine parts.

Tests have shown that the oil doesn't stop lubricating just because TBN is low.



Just my humble $0.02

 

[OVERKILL]

Well, a VOA on the oil to know what the virgin levels of TBN/TAN are is a good place to start.

And no, you aren't wrong, generally, as long as you have a good idea of what the virgin figures are, tracking them with TBN/TAN of the used product, along with of course the other condemning parameters is staying the course for determining suitable OCI length for that fluid in your application.

Now, this is of course in the context of maximizing your OCI. If you are doing the BITOG UOA dance where you are just obsessing about contaminants and not planning on running extended drains where this stuff is important, then it's a waste of money if you are paying extra for it.

 

[irv]

Originally Posted By: Artem
From my years and years of research in trying to understand your original question, I'd say that the TBN / TAN crossover condemnation point is probably accurate from a scientific oil analysis standpoint of the lubricant but over the years companies noted that although TAN is higher then TBN the oil is still able to do its job up to a point and can TECHNICALLY be used further without severe consequences... at least in the short term (during the typical warranty period).

Also engine design is a major player here. If an engine runs hot naturally and has hot spots inside the engine, then the high TAN and low TBN service interval will result in carbon / sludge build up because the reality is... the oil can't handle the build up chemically.

Now in the same scenario in an efficient, well designed engine, no problems will show up because the highly acidic oil isn't being baked into the pores of the engine parts.

Tests have shown that the oil doesn't stop lubricating just because TBN is low.



Just my humble $0.02


Interesting.

Thanks.

 

[WobblyElvis]

I have taken the TBN down to 1.0 according to a Blackstone UOA and they still suggest I could use the oil longer. All my cars are high mileage and they are getting brown/red inside but no sludge buildup that I can find with the valve cover off.

 

[Artem]

I've done the same with several cars over the years and those engines still had bare, clean aluminum showing thru the fill hole.

 

[Artem]

Originally Posted By: OVERKILL
Well, a VOA on the oil to know what the virgin levels of TBN/TAN are is a good place to start.

And no, you aren't wrong, generally, as long as you have a good idea of what the virgin figures are, tracking them with TBN/TAN of the used product, along with of course the other condemning parameters is staying the course for determining suitable OCI length for that fluid in your application.

Now, this is of course in the context of maximizing your OCI. If you are doing the BITOG UOA dance where you are just obsessing about contaminants and not planning on running extended drains where this stuff is important, then it's a waste of money if you are paying extra for it.


Well said but isn't there a difference between good and bad TAN? Say some blender starts the oil off with a high virgin TAN to act as a cleaner to quickly rinse thru the engine and flush previous deposits, etc and the TAN then drops off once the original acidic additives do their job and wear out, so to speak. After that, the BAD TAN starts to rise as the oil becomes loaded with contaminants.

So I think there's a difference between virgin TAN as part of the original additive formula and the resulting acidic soup that drains out once the oil is toast towards the end of the interval.

 

[OVERKILL]

Originally Posted By: WobblyElvis
I have taken the TBN down to 1.0 according to a Blackstone UOA and they still suggest I could use the oil longer. All my cars are high mileage and they are getting brown/red inside but no sludge buildup that I can find with the valve cover off.


You should try Toromont.

 

[OVERKILL]

Originally Posted By: Artem

Well said but isn't there a difference between good and bad TAN? Say some blender starts the oil off with a high virgin TAN to act as a cleaner to quickly rinse thru the engine and flush previous deposits, etc and the TAN then drops off once the original acidic additives do their job and wear out, so to speak. After that, the BAD TAN starts to rise as the oil becomes loaded with contaminants.

So I think there's a difference between virgin TAN as part of the original additive formula and the resulting acidic soup that drains out once the oil is toast towards the end of the interval.


Yes, that's why I mentioned you want a VOA so that you at least know where the oil starts off. As I said in my first post in this thread, some oils have high virgin TAN, just like some have high virgin oxidation, the latter being an artifact of base oil selection usually. Having a VOA, and you know your virgin TAN is 10, well if TBN is 8, you've already crossed, so you know that isn't right, LOL! At that point one SHOULD be able to roughly figure the relationship based on those two numbers and that you could, roughly, subtract the virgin TAN from the end TAN to get a better fudge-factored "real" TAN figure for what has accrued over the OCI. Though my impression is that this isn't likely foolproof and that oils with high virgin TAN numbers are simply harder to track in this manner.

Per your posit, one would almost need to do incremental samples to determine if this behaviour is as expected with an increase/decrease relationship, whether there is a precipitous drop followed by a gradual increase, or whether the whole thing is cumulative.

Looking at back at some of the old AMSOIL VOA's and UOA's, including one of yours, I see a virgin TAN of 4.6 for one of their oils and your UOA showed a TAN of 4.0 with a TBN of 3.0 after only 5,000 miles. So there obviously needs to be some sort of fudge factor worked into that relationship when presented with a product that samples in that manner

 

[camrydriver111]

If TAN/TBN ratio was a measure of acidity then the TAN/TBN crossover makes sense. However it's not a direct measure of acidity.

I'll give you an example. Hydrochloric acid is more acidic than acetic acid. pH of 1 M HCl is 0, while the pH of 1 M acetic acid is around 2.5. If you have 1 M acetic acid and titrate it with NaOH you will get a result of 1 Molar. If you have 1 M of hydrochloric acid and titrate it with NaOH you will also get a result of 1 M. If you just look at total NaOH to neutralize the acid they are equally acidic, but they are not.

TAN is determined by titration by NaOH. Obviously the oils have additives that can react when you titrate them with NaOH. That doesn't mean the oil is acidic.

https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/4775863/VOA_BMW_Twin_Power_Turbo_5W30_

TBN of that oil is 6.7, and TAN is 4.1. If you follow the TBN/TAN logic you should dump that oil after about 3k miles when the crossover occurs instead of 15k miles like BMW recommends.

I think TAN could also be easily influenced by operating conditions. For example if you have condensation in the engine from winter driving or fuel dilution it might increase TAN. They didn't label this graph completely, however if the x-axis is miles then the TAN is highly unpredictable compared to TBN.

Source: https://www.machinerylubrication.com/Read/2170/oil-drain-interval-tan-tbn

They advocate for the TAN/TBN crossover point in this article and recommend changing at 65%. You could take this as proof of the TAN/TBN theory but I will trust Blackstone, BMW, Exxon, etc. over Polaris Laboratories LLC. If you subtract the initial TAN of the oil (which they don't), the TBN/TAN crossover will actually occur when TBN is close to depletion. So that could be the fudge factor you were talking about.

UOAs and real world tests also don't support the TAN/TBN crossover theory. We don't see viscosity changes or increased wear in UOAs when TAN becomes greater than TBN. We also don't see engine wear or sludge from people running extended OCIs and monitoring TBN.

 

[OVERKILL]

Originally Posted By: camrydriver111


UOAs and real world tests also don't support the TAN/TBN crossover theory. We don't see viscosity changes or increased wear in UOAs when TAN becomes greater than TBN. We also don't see engine wear or sludge from people running extended OCIs and monitoring TBN.


No, but it is supported by some manufacturers.

I know in Doug Hillary's testing he ran TBN down to about ~2 and TAN was significantly higher with no adverse effects that he observed upon tear-down.

 

[irv]

Thanks for the info, guys.

I had no idea TAN would be a positive in new oils from the get go. I assumed it started at zero and the TAN was a measure of how much acid had accumulated over the course of an oil run from new to being spent/used up.

 

[JAG]

No general correlation seems to exist between TAN and corrosivity toward metals. Low TAN, no problem. High TAN, may be a problem or may not.

https://books.google.com/books?id=i5nolx...ing&f=false

http://www.coqa-inc.org/docs/default-source/meeting-presentations/Devils_Tower_TAN_SAT_Feb_2007.pdf

 

[irv]

Originally Posted By: JAG
No general correlation seems to exist between TAN and corrosivity toward metals. Low TAN, no problem. High TAN, may be a problem or may not.

https://books.google.com/books?id=i5nolx...ing&f=false

http://www.coqa-inc.org/docs/default-source/meeting-presentations/Devils_Tower_TAN_SAT_Feb_2007.pdf


I guess to play it safe, one should just change out their oil before the numbers approach one another or begin to cross?

And, if I am guessing correctly, the only way to know, unless you did a mid run UOA (most wouldn't I assume?) is to go by previous UOAs?

Hardly anything for me to worry about doing semi annual OC's but this was, for the most part, (although a bit confusing/inconclusive), an educational post for me.

 

[Artem]

That is how it was viewed many years ago. These days most will say that the TAN / TBN crossover isn't necessary the end all be all tell tale sign of an expired lube. Need to look at wear rates and the rest of the fluid condition such as viscosity, and fuel dilution or contamination.

At the end of the day, if wear is good, most on here will agree that running the TBN down to 1-2.0 is safe pretty much regardless of where TAN stands in relation.

So take that with a grain of salt...

 

[DuckRyder]

The biggest issue with TBN/TAN crossover is that it is expensive to measure unless you have free access to UOA’s. You’re going to drop 50 bucks on a UOA with TBN/TAN @ Blackstone and ALS will not even do it on engine oil (or maybe that was PC, anyway) that is a jug or Mobil 1 AP at regular price, or nearly 2 of just about any typical synthetic on rollback or a lot of conventional.

Factor in that there are 2 methods of TBN (which is why ALS flags at 2 and Blackstone at 1) and that TAN is basically a test that tells you investigate further and it is a bit too messy to draw any real conclusion from IMO.

There certainly isn’t a hard and fast rule.

UOA’s are wasteful on passenger cars IMO. Interesting perhaps, maybe even mildly useful, but when you consider the cost, time, mailing I’m increasing convinced the least wasteful way is to simply change the oil on a reasonable schedule with a reasonable oil. Sure a piece of heavy equipment or OTR truck that holds 10 + gallons sure, but a 4-6 QT passenger car or truck - waste...

I know this is all very un BITOG like, but that is the way I see it. This being BITOG we are heavily invested in the UOA thing, we NEED for it to mean something...

 

[Hammehead]

Bitogers do UOAs in their small engines, not for economic reasons, more to proving a point or mere curiosity about hidden problems to be catch early. You should know that already.

 

[Artem]

Well said. I'm sure a good 90% of said curiosity UOA are to see how the oil is doing after X amount of miles and to check for abnormal engine wear. No good bang for the buck, if you really think about it. I'm sure doing 3,000 mile OCIs with $10 conventional oil is cheaper then some high end PAO or Ester oil + UOA in an attempt to extend the interval by a few thousand miles.