Help me understand TAN

[Jake777]

So is it correct to say that TBN is the oils ability to neutralize acid and TAN is how much acid has been neutralized already? Also is it important to change oil or does oil loose it's ability to neutralize acid as TAN and TBN intersect? What if per say you had TBN at 4.0 but TAN at 6.0 would you say it's time to change?

 

[Quattro Pete]

The oil's acidity increases due to various processes taking place inside an engine. TAN is a measure of this acidity.

As far as TAN vs TBN, you'll get different answers on this. Some people will say TAN is not very relevant to a gasoline engine. Then there are new oil technologies that have fairly high starting TAN values, so you really need to be comparing increases in TAN to the virgin sample of the particular oil that you are using.

But for starters, here is one link you might find of some interest:
http://www.machinerylubrication.com/Read/2170/oil-drain-interval-tan-tbn

 

[A_Harman]

I've been reading BITOG for 5 years now, and am less certain now about how TAN & TBN relate to oil changes than when I started. I was taught at Cummins was that if TBN dropped below 2.0, the oil should be changed. Then I started reading Blackstone used oil analysis on BITOG, and they always say to run the TBN down to 1.0 before changing oil. Then I started getting used oil analysis done at Polaris labs, and they say to change oil when TBN gets down to 35% of virgin. And other people have said to change when TAN exceeds TBN. Still other people have said to change when TAN increases from virgin as much as TBN has dropped.

I would just stay with the original Cummins instruction, and change oil when TBN gets close to 2.0. But realistically, I haven't had TBN trigger an oil change on my Dodge truck. Iron wear metals trigger that one when it gets to 100 ppm, or if it gets to 24,000 miles on the oil, then I dump it. On the Camaro, I went past the Polaris 35% recommendation a few times, and ran TBN down close to 2.0, and it seems none the worse for it.

 

[A_Harman]

Originally Posted By: Quattro Pete
The oil's acidity increases due to various processes taking place inside an engine. TAN is a measure of this acidity.

As far as TAN vs TBN, you'll get different answers on this. Some people will say TAN is not very relevant to a gasoline engine. Then there are new oil technologies that have fairly high starting TAN values, so you really need to be comparing increases in TAN to the virgin sample of the particular oil that you are using.

But for starters, here is one link you might find of some interest:
http://www.machinerylubrication.com/Read/2170/oil-drain-interval-tan-tbn


Nice article. Thanks for this, QP.
The article was written by Polaris, and it explains the basis of their 35% TBN recommendation. This apparently applies if the lab is using the ASTM D-4739 method.

 

[Pontual]

Originally Posted By: Jake777
So is it correct to say that TBN is the oils ability to neutralize acid and TAN is how much acid has been neutralized already? Also is it important to change oil or does oil loose it's ability to neutralize acid as TAN and TBN intersect? What if per say you had TBN at 4.0 but TAN at 6.0 would you say it's time to change?


Well, if the acid that has already being neutralised, is what gives the TAN#, then it is harmless, so a 1TBN would be enough? But where the salt plus water went?

 

[UNC151]

Originally Posted By: Pontual
Originally Posted By: Jake777
So is it correct to say that TBN is the oils ability to neutralize acid and TAN is how much acid has been neutralized already? Also is it important to change oil or does oil loose it's ability to neutralize acid as TAN and TBN intersect? What if per say you had TBN at 4.0 but TAN at 6.0 would you say it's time to change?
Well, if the acid that has already being neutralised, is what gives the TAN#, then it is harmless, so a 1TBN would be enough? But where the salt plus water went?
Many oils do not start with a 0.0 TAN reading and therefore the acid will never be fully neutralized. The TAN will continue to climb as the TBN continues to drop. The **seemingly** unknown (and it has been discussed at length here) is at what ratio should the oil be changed--if one is only considering the TAN/TBN and no other factors.

 

[Pontual]

TAN on new oil is dependant on final add pack. Other new have basic add pack. Thats why some are against mixing oils... Most modern oils are basic in ph when new.

 

[bobbydavro]

TAN on fresh oils will be 2.5-3.

I dont really worry about TBN as its a measure of the oils base. What is important is how much acid is in the engine. This combined with Oxidation and viscosity gives an indication when oils reaches end of life.

There is no rule about crossover or TBN% of fresh etc.

 

[weasley]

TAN is not a measure of acid that has been neutralised - it is a measure of the presence of un-neutralised acidic species. This includes a number of chemical types, not all of which are highly or even moderately corrosive to the metals in an engine. However, in general terms, higher TAN is worse.

Originally Posted By: bobbydavro
There is no rule about crossover or TBN% of fresh etc.


Bingo. See this post I made (wow, nearly 3 years ago!) for my thoughts on TBN and the TBN/TAN crossover thing.

 

[Joe90_guy]

One source of TAN in fresh oils is PIBSA (Poly Iso-Butane Succinic Acid). PIBSA can have an individual TAN of around 100 so it's pretty acidic.

Some vile, grubby people add PIBSA to oil to pass VW seals tests and manipulate the Minor Mod Rules to make this appear acceptable. It's not.