Oil TBN and TAN

[mechanicx]

If TBN is the total base number and TAN is the total acid number, then shouldn't they be the same? How is it an oil can be both basic and acidic in total at the same time? So shouldn't TBN equal TAN and the ratio of TBN to TAN be 1? Or maybe it should be the inverse. If TBN is above 7 then TAN should be below 7. And if TBN is below 7, TAN should be above 7?

I know this is wrong, I'm just asking.

 

[Gary Allan]

http://www.usoilcheck.com/oilchek/services/used+oil+analysis/tutorial/tbn+tan.asp


I'm not well versed on it myself since we don't often see the two in comparison, but the nearest I can figure is that TAN measures the presence of the compounds/materials that evidence acids. It's the point where they're exceeding the neutralization point of the TBN that you're concerned about.

 

[Doug Hillary]

Hi,
mechanix - The two number are "in conflict" if you like

The TBN represents the alkalinity and the lubricant's ability to neutralise acid (D2896 or D4739). A high TBN was required with high sulphur levels in fuels. Typically as the TBN is increased the SA level rises - this is undesirable in certain engine families. So Blenders have a problem - new chemicals have somewhat solved this and we see lower levels of TBN in new products. Ideally we need a mid range TBN and a low SA level for most modern engine families

The TBN falls with use and a condemnation point of 1 D4739 or 2 D2896 is used by a number of engine Manufacturers

The TAN measures the build up of acidic contaminants and is a rising number. There may be a TAN limit in some cases and the two do not form a close and predictable ratio in use - or I have never detected it!

With diesel engine used oil analysis I have always used both - this has been to confirm one to the other. Lab results do vary and people make mistakes

I never set a TAN limit for my engines nor had one set by an engine Manufacturer

The typical levels at OC for me were TAN 6 and TBN 2 (D4739). I have detected many Lab errors over the years with the TBN being inconsistent in decline - this can be detected by movements with the TAN. This is why trending used oil analysis - especially within similar engine families - is very important

In heavy high speed diesel engines a low TBN was never a lubricant condemnation point for me - it was always soot or iron levels - or both!

 

[mechanicx]

Originally Posted By: Doug Hillary
Hi,
mechanix - The two number are "in conflict" if you like

The TBN represents the alkalinity and the lubricant's ability to neutralise acid (D2896 or D4739). A high TBN was required with high sulphur levels in fuels. Typically as the TBN is increased the SA level rises - this is undesirable in certain engine families. So Blenders have a problem - new chemicals have somewhat solved this and we see lower levels of TBN in new products. Ideally we need a mid range TBN and a low SA level for most modern engine families


Hey Doug, By SA do you mean sulfuric acid or something else?

Quote:
The TBN falls with use and a condemnation point of 1 D4739 or 2 D2896 is used by a number of engine Manufacturers

The TAN measures the build up of acidic contaminants and is a rising number. There may be a TAN limit in some cases and the two do not form a close and predictable ratio in use - or I have never detected it!


So TBN and TAN do work somewhat in inverse though?

Quote:
With diesel engine used oil analysis I have always used both - this has been to confirm one to the other. Lab results do vary and people make mistakes

I never set a TAN limit for my engines nor had one set by an engine Manufacturer

The typical levels at OC for me were TAN 6 and TBN 2 (D4739). I have detected many Lab errors over the years with the TBN being inconsistent in decline - this can be detected by movements with the TAN. This is why trending used oil analysis - especially within similar engine families - is very important

In heavy high speed diesel engines a low TBN was never a lubricant condemnation point for me - it was always soot or iron levels - or both!


So I'm starting to think TAN is not so important to get in an UOA especially with a gasoline engine as long as you have an accurate TBN. Would you say that's fair? I guess that's why Oil Analyzers doesn't offer TAN and most people don't get TAN tested even if it is offered? It seems like you'd want to know TAN with a diesel since I heard it create a lot of acid, but I see you're saying soot is a biggr problem with them anyway.

 

[mechanicx]

Originally Posted By: Gary Allan
http://www.usoilcheck.com/oilchek/services/used+oil+analysis/tutorial/tbn+tan.asp


I'm not well versed on it myself since we don't often see the two in comparison, but the nearest I can figure is that TAN measures the presence of the compounds/materials that evidence acids. It's the point where they're exceeding the neutralization point of the TBN that you're concerned about.


Yeah that link was an interesting and concise read. I noticed they suggest that a TBN below 3 is too low and signals a need for an oil change. I wonder if they are good at UOA and what they charge? I couldn't find prices on their site. I noticed they didn't do TAN either. I'm sarting to think TAN doesn't really directly tell you much now.

 

[Doug Hillary]

Hi,
mechanix - SA is Sulphated Ash
I suppose there is an inverse realtionship at some level - it would only be determined by a matrix of factores

I believe that both TAN and TBN have a great significance in highly utilised engines and with extended OCIs - trended of course

IME the condemnation factors of soot and iron outweight all else

Best wishes

 

[mechanicx]

OK SA meant sulfated ash. I couldn't figure what the abreviaton was for other than sulfuric acid, so my next question was going to be why would higher TBN increase sulfuric acid lol. It all makes sense now.

So I take it the iron you mention is too small to be caught in the oil filter but big enough to cause engine wear?

 

[Doug Hillary]

Hi,
mechanicx - This is a brief description. The progression of debris starts with the intake screen then moves to the FF filter. This is one reason why modern lubricants have excellent detergency - keeping the intake screen clean is extremely important for oil flow purposes

Items that are stopped at the FF filter are a product of the media's design. What circulates is a mixture of "items" too small to be caught by the FF filter - typically less than 15micron or so (some centrifuge oil cleaners may remove sub-micron sized contaminants). Some modern synthetic media FF filters may have an efficiency of nearly 70% with 5micron debris

In the case of wear metals (in ppm) these circulate until the lubricant is drained. What is left behind will contaminate the new lubricant at startup

Iron levels above 150ppm are considered (by some engine Manufacturers) to be at a level that may promote excessive wear in some components. It is the same with soot. Soot must not agglomerate - this can lead to excessive deposit formation - and excessive wear. A modern HDEO will tolerate soot up to around 3% - some synthetic versions can handle up to double that figure

 

[mechanicx]

Originally Posted By: Doug Hillary
Hi,
mechanicx - This is a brief description. The progression of debris starts with the intake screen then moves to the FF filter. This is one reason why modern lubricants have excellent detergency - keeping the intake screen clean is extremely important for oil flow purposes

Items that are stopped at the FF filter are a product of the media's design. What circulates is a mixture of "items" too small to be caught by the FF filter - typically less than 15micron or so (some centrifuge oil cleaners may remove sub-micron sized contaminants). Some modern synthetic media FF filters may have an efficiency of nearly 70% with 5micron debris

In the case of wear metals (in ppm) these circulate until the lubricant is drained. What is left behind will contaminate the new lubricant at startup

Iron levels above 150ppm are considered (by some engine Manufacturers) to be at a level that may promote excessive wear in some components. It is the same with soot. Soot must not agglomerate - this can lead to excessive deposit formation - and excessive wear. A modern HDEO will tolerate soot up to around 3% - some synthetic versions can handle up to double that figure


I guess what I was wondering is when you see wear metals on a used oil analysis, what micron size would they typically be? Smaller than 5 microns and too small for the FF filter to catch them all but big enough to cause wear I'm assuming? Also I assume when the iron levels are high it is a sign that the oil is not protecting against wear as well.