TAN VS TBN CROSSOVER

[Smokefan1977]

With some reading Im a little confused on this subject. As i understand it in and oils life it is possible for TAN and TBN to crossover. When this happens the product can show active TBN, but actually pretty much be used up. If Im off on this please help me understand as i don't really see a purpose of a TBN to determine oil life without having a TAN aswell.

Thanks guys

 

[Artem]

It's a confusing subject to me as well and no one seems to have an accurate and complete answer that is FACT.

The Lab says one thing, respected members say another.

 

[Samilcar]

Count me in as one of the confused. Some say the TBN-TAN crossover point can be used to determine the useful life of the oil, others say that that's no longer the case.

 

[btanchors]

I would also love to hear some information from someone authoritative. Some of the new oils, such as the recent VOA I did on Amsoil's ZRT oil, have TANs that start out high - like 4.8. When you combine this with the trend of oils that start out with lower initial TBNs, it won't take long for the two to cross over.

 

[Quattro Pete]

Originally Posted By: btanchors
I would also love to hear some information from someone authoritative.

The only thing that I'm aware of is this article from Polaris labs:
http://www.polarislabs.com/pdf/optimizing-drain-intervals-using-tbn-vs-tan.pdf

However, I believe this is talking mainly about diesel applications. Applicability to gasoline engines is questionable.

 

[Jim Allen]

Originally Posted By: Quattro Pete
Originally Posted By: btanchors
I would also love to hear some information from someone authoritative.

The only thing that I'm aware of is this article from Polaris labs:
http://www.polarislabs.com/pdf/optimizing-drain-intervals-using-tbn-vs-tan.pdf

However, I believe this is talking mainly about diesel applications. Applicability to gasoline engines is questionable.


Polaris said it works the same way for gassers and I can't think of why it would be questionable. We had this discussion last year and here is the link:

TBN/TAN Crossover

It's probably not reliable to run to the ragged edge but I think it's safe as a rule-of-thumb... i.e. run to 35% of starting TBN... but it would be best to run a TAN test or two along with TBN to verify on YOUR particular engine.

 

[Quattro Pete]

Originally Posted By: Jim Allen
It's probably not reliable to run to the ragged edge but I think it's safe as a rule-of-thumb... i.e. run to 35% of starting TBN... but it would be best to run a TAN test or two along with TBN to verify on YOUR particular engine.

So, what do you say in cases like Artem's?

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2427852#Post2427852

He's down to about 30% of his initial TBN. His TAN is more than twice the TBN, but it's hard to tell whether the oil is hurting anything. Blackstone recommends going longer next time.

 

[Samilcar]

My last UOA looked similar to that. After 11,000 miles on the oil, the TBN was 1.4 and TAN was 6.0 with all wear metals and insolubles looking OK. Blackstone recommended going to 12,500 miles for the next OCI. I've decided to back off to 10,000 miles.

 

[Jim Allen]

I think you need to know what the starting TAN was for the oil and that point is "Zero"... at least I think that's how it works. Like you said, it's hard to know if it was hurting anything.

Read This: Oil Lab

I have only skimmed it so far but will read it thoroughly when I can. Seems to show that TBN may not be as accurate an indicator as some of us might like, but it varies depending on what additives are used. I CAN be accurate or it might not.

 

[OldCowboy]

Originally Posted By: Quattro Pete
Originally Posted By: btanchors
I would also love to hear some information from someone authoritative.

The only thing that I'm aware of is this article from Polaris labs:
http://www.polarislabs.com/pdf/optimizing-drain-intervals-using-tbn-vs-tan.pdf


I think the last paragraph of this paper is important: "Monitoring TBN, Viscosity, Oxidation and Nitration simultaneously and changing both the oil and filters when contamination from dirt, coolant, fuel dilution or soot reaches critical alarm limits is ultimately the best way to determine optimal engine oil drain intervals regardless of the time on the oil."

Notice they don't mention TAN in this statement. In the article they note that TAN and TBN cross-over when TBN reaches 35% of the beginning level.

However, we have numerous UOAs that would seem to indicate that Polaris' recommendation is conservative and one can safely run oil to approximately 20% of the starting TBN level.