TBN

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Higher is better to a point. This is where the pH starts out in a motor oil. Base is the opposite of Acid. Base raises pH and Acid lowers pH. For example, pH of 7 is neutral as in water(H2o). So it the case of motor oil, the more acidic the oil becomes, the lower the pH becomes. I guess that around a pH of <2, the oil is becoming too acidic for aluminum. EDIT: Not sure that I said all of that correctly. But from my lab experience, I know what I am trying to say.
 
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Higher is better as it allows the oil to resist acid build up longer. Higher isn't really that important if you don't do long oil change intervals.
 
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Originally Posted by FordCapriDriver
Some say that when the TBN drops below 3 it's time to change.
I would say between 1 and 2 you should change. Its not linear also.
 
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The TBN,s were from 2.7 to 3.4. 2.7 was on 6551 oci and 3.4 was on 8988 oci. That 8988 was after taking a long road trip. wonder what TBI of new Mobil1 would be?
 
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Originally Posted by borgward
wonder what TBI of new Mobil1 would be?
Which Mobil1? Look at the VOAs we have on this site. They'll usually show you that info.
 
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Originally Posted by Char Baby
Higher is better to a point. This is where the pH starts out in a motor oil. Base is the opposite of Acid. Base raises pH and Acid lowers pH. For example, pH of 7 is neutral as in water(H2o). So it the case of motor oil, the more acidic the oil becomes, the lower the pH becomes. I guess that around a pH of <2, the oil is becoming too acidic for aluminum. EDIT: Not sure that I said all of that correctly. But from my lab experience, I know what I am trying to say.
Sort of in the right place, but not technically correct. pH is a measure of acidity and alkalinity in an aqueous medium ("pH" literally means "-log10[H+]", or minus log base ten of the concentration of hydrogen ions). Oil is not an aqueous medium so the concept of 'acid' and 'alkali' is somewhat different and can not be measured or expressed as pH. TBN is a measure of an oil's alkaline reserve, which is used to neutralise acids. High or low is not good or bad because it depends on a number of factors as to what TBN is appropriate. Diesel engine oils tend to have higher TBN as diesel engines generate more acidic species in combustion. Longer drain oils have higher TBNs simply to allow them to carry on for longer. TBN drops in use, so the higher your starting point, the longer you go until the TBN is depleted. High TBN in a UOA isn't always a good thing - the TBN is there to do a job - neutralise acids. If the TBN stays high then it isn't doing anything, meaning either there are no acids to mop up or that the acids are present but not being mopped up by the TBN. This idea of TBN retention is all very well, so long as the TBN is actually doing what its there for.
 
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Originally Posted by weasley
High TBN in a UOA isn't always a good thing - the TBN is there to do a job - neutralise acids. If the TBN stays high then it isn't doing anything, meaning either there are no acids to mop up or that the acids are present but not being mopped up by the TBN.
This is why it's helpful to know TAN as well.
 
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Originally Posted by borgward
What is the significance of the TBN number in an oil report? is higher or lower better?
TBN = Total Base Number. As mentioned, it is the protective additives in the oil. Too low is bad; I base my condemnation level on Blackstone's recommendation of no lower than 1.0, going conservative at 1.5. Most of my runs never reach that level. On the UOA, compare the TBN with the starting TBN of the oil; but that is not all to look at to determine interval. Check also the viscosity to see if it has thickened or thinned out of grade. Also check for coolant, water, and insolubles, all of which tell more about your oil's condition. I might suggest some reading of UOA threads, plenty of information there to assist in learning what you want to know.
 
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Originally Posted by ZZman
Higher is better as it allows the oil to resist acid build up longer. Higher isn't really that important if you don't do long oil change intervals.
True having a high(er) TBN is desirable when doing long oci's but even on short oci's a high(er) TBN can be desirable. If you have excessive blow by or dilution, these can accelerate oxidation and the formation of harmful acids.
 
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Originally Posted by weasley
High TBN in a UOA isn't always a good thing - the TBN is there to do a job - neutralise acids. If the TBN stays high then it isn't doing anything, meaning either there are no acids to mop up or that the acids are present but not being mopped up by the TBN. This idea of TBN retention is all very well, so long as the TBN is actually doing what its there for.
Indeed reserve alkalinity is important and I've personally NEVER seen a UOA where the oils reserve alkalinity didn't drop by some amount. Every engine experiences blow by on some level... it's what's in the blow by that creates acids in the crankcase. I don't see how an oils reserve alkalinity could be unaffected by this most basic of engine processes. But maybe I'm missing something..🤔
 
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12,722
Location
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Originally Posted by SirTanon
Originally Posted by Char Baby
Originally Posted by FordCapriDriver
Some say that when the TBN drops below 3 it's time to change.
220/221.... wink
Mr. Mom reference? LOL
You know the movie? laugh
 
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Location
Phoenix, Arizona - USA
Originally Posted by Char Baby
Originally Posted by SirTanon
Originally Posted by Char Baby
Originally Posted by FordCapriDriver
Some say that when the TBN drops below 3 it's time to change.
220/221.... wink
Mr. Mom reference? LOL
You know the movie? laugh
But, of course I do! "Wow! What did you use, a 38?" ".. 38, 39.. whatever it took" Love that scene!
 
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Location
UK
Originally Posted by Mad_Hatter
Originally Posted by weasley
High TBN in a UOA isn't always a good thing - the TBN is there to do a job - neutralise acids. If the TBN stays high then it isn't doing anything, meaning either there are no acids to mop up or that the acids are present but not being mopped up by the TBN. This idea of TBN retention is all very well, so long as the TBN is actually doing what its there for.
Indeed reserve alkalinity is important and I've personally NEVER seen a UOA where the oils reserve alkalinity didn't drop by some amount. Every engine experiences blow by on some level... it's what's in the blow by that creates acids in the crankcase. I don't see how an oils reserve alkalinity could be unaffected by this most basic of engine processes. But maybe I'm missing something..🤔
Just because something in the oil reacts with the reagents in the TBN test does not mean they will necessarily react with the acids in the oil. Indeed there are different TBN methods that give different results because they use more or less aggressive reagents. TBN comes from a variety of sources, from inorganic salts in the detergents to organic molecules such as dispersants and antioxidants. These will react at different rates with different acids meaning that depletion rates will vary dependent on where the TBN is coming from. It's possible you could have some TBN that will show up in a ASTM D2896 test that won't actually react with engine-derived acidic species. Yes, TBN will always tend to fall but you can have a slow TBN drop AND a dramatic TAN rise at the same time.
 
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