Truth about TBN?

[HKPolice]

http://www.usoilchek.com/Used_Oil_Analysis/Pages/TBN-TAN.aspx

Quote:
TAN increases in service as TBN decreases. The point at which these two numbers meet has been indicated as the maximum useful oil change interval for that type of engine in that type of service. Studies have shown that when TAN exceeds TBN, engine wear accelerates at abnormally high rates.


I see a lot of UOA where people run extended drains down to 1-2 TBN without doing a TAN measurement, even Blackstone labs recommends going down to 1 TBN. I think this is more dangerous than what most people think. Take a look at this Mobil 1 EP VOA:

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2260688

It starts off with a high TAN of 3.4 and people are running this oil down to 2 TBN without doing a TAN measurement, which could easily be 5-6+ by then.

I personally don't feel comfortable with more than 7-8k intervals regardless of the oil. Should we be paying more attention to the TAN/TBN ratio rather than just the absolute TBN? It makes more sense to me to look at the ratio.

 

[zerosoma]

Agreed, good insights.

 

[Donald]

Most people do not even get TBN unless they are going 10K+. Blackstone charged extra for TBN. Probably even more for TAN.

 

[bigjl]

I have noticed that most of the low saps oils, specifically 5w30, have low TBN out of the box.

And are intended for extended drains as normal in most of Western Europe.

Ocis can be as high as 18k or 2 years.

I can't leave it that long to be honest.

 

[tig1]

"Dangerous" is not normally associated with oil. However you can relax, because 10K OCIs and beyond are done here all the time in engines that see 200,300K miles(not KMs) and never show signs of wear. That's been my history with M1 oils for 36 years.

 

[A_Harman]

Blackstone is always advocating running TBN down to 1.0, but that is not a universal recommendation. I get my oil analyses done at Polaris, and they recommend dumping the oil at 35% of virgin TBN. I have asked Polaris to do TAN readings on my samples, but they won't do TAN for any other than natural gas engines. Don't ask me why.

And there are other strategies. When I was a development engineer at Cummins about 20 years ago, the doctrine was to change oil when TBN dropped to ~2, or when TAN exceeded TBN, whichever came first.

 

[btanchors]

Many synthetic oils start out with a high TAN, sometimes over 4.

If you take such an oil, with a high starting TAN, I find it hard to believe that when TBN reaches 4, it's time to condemn the oil.

My thinking is it might be better that when the INCREASE in TAN exceeds the TBN, this might be a better measurement, at least for oils with a high starting TAN.

For example, suppose an oil has a starting TAN of 3.8. Then you use this oil in some application and perform a VOA.

The TAN comes out to 5.9 and TBN 2.0. You would condemn that oil because the increase in TAN (5.9 - 3.8 = 2.1) exceeds the TBN of 2.0.

Thoughts?

 

[Quattro Pete]

Originally Posted By: HKPolice
I see a lot of UOA where people run extended drains down to 1-2 TBN without doing a TAN measurement, even Blackstone labs recommends going down to 1 TBN. I think this is more dangerous than what most people think.

Dangerous in what way? The article suggests accelerated wear, but most of the time we do not see elevated wear metals in these UOAs where TBN has reached such low levels.

By the way, the subject of using TBN-TAN relationship has been discussed here on BITOG a number of times before. Also, the lab I use (wearcheck) flags the sample as "ABNORMAL" anytime TAN reaches 80% of TBN, so they're even more conservative in this area than what the article you linked to suggests.

FYI, here's a link to one of many previous discussions:
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1970704

 

[Doog]

I 100% agree with the theory behind the TBN/TAN relationship. Great post!!

 

[901Memphis]

Blackstone uses a different method for TBN than the other Labs. It's conservatively low.

 

[Quattro Pete]

Most labs nowadays use the same TBN test method (ASTM D4739).

 

[Pablo]

Originally Posted By: btanchors
Many synthetic oils start out with a high TAN, sometimes over 4.

If you take such an oil, with a high starting TAN, I find it hard to believe that when TBN reaches 4, it's time to condemn the oil.

My thinking is it might be better that when the INCREASE in TAN exceeds the TBN, this might be a better measurement, at least for oils with a high starting TAN.

For example, suppose an oil has a starting TAN of 3.8. Then you use this oil in some application and perform a VOA.

The TAN comes out to 5.9 and TBN 2.0. You would condemn that oil because the increase in TAN (5.9 - 3.8 = 2.1) exceeds the TBN of 2.0.

Thoughts?


You are holding your head correctly. This paragraph is not only over simplifying, it's a bit wrong.

Quote:
TAN by itself is of limited value in determining oil condition of an engine oil due to the fact that it represents a combination of different chemical characteristics. The acid-like nature of anti-wear additives found in most modern engine oils cause a high initial TAN.


The above part seems wholly true.


Quote:
Greatest benefit is derived from the TAN by comparing it to the TBN. TAN increases in service as TBN decreases. The point at which these two numbers meet has been indicated as the maximum useful oil change interval for that type of engine in that type of service. Studies have shown that when TAN exceeds TBN, engine wear accelerates at abnormally high rates.


Yes and no. I disagree - I don't think that is at all the "Greatest benefit" derived from TAN. TAN increases from 4 to 5, and TBN drops from 10 to 5, the oil is condemned? No way.

I want to see the studies that show the last sentence - I think they condensed something like "when TAN is exceedingly high, engine wear accelerates at abnormally high rates" into their own statement (above)

 

[CarbonSteel]

Blackstone does not state that TAN is high until in the 8 to 9 range (if memory serves) and they measure TBN differently than Polaris, WearCheck, etc. There is nothing wrong with that, it is just different. I have ran the oil many times until the TAN has crossed TBN and I have not seen "dangerous" or abnormal wear rates. In fact, quite the opposite--I ran M1 for 15K and it produced the best UOA to date and I have UOA'ed every OC. The TBN was 2.9 and the TAN was 5.0; IMHO the line between the two is much farther apart that most believe.

 

[JAG]

If one is getting a UOA with TBN, wear metal concentrations are also measured. Corrosive wear generates small particles that UOAs quite accurately measure. So the necessary data for determining if the oil's acid/base situation is ok or not can be gleaned from the wear metal concentrations. Old rules of thumb for condemnation of oil based on TBN or TAN or some combination of them may not apply in many cases with today's oils, fuels, and engines. Additives that inhibit corrosion are one of the crucial factors that are frequently ignored in these discussions.

 

[Quattro Pete]

Originally Posted By: 2010_FX4
and they measure TBN differently than Polaris, WearCheck, etc.

Not sure about Polaris, but WearCheck now uses the same ASTM test method as Blackstone.

 

[A_Harman]

Originally Posted By: JAG
Old rules of thumb for condemnation of oil based on TBN or TAN or some combination of them may not apply in many cases with today's oils, fuels, and engines.


This hints at something I was thinking about: consult the oil manufacturer as to what TBN/TAN relationship should be used to trigger an oil change.