Interpreting the TBN

[paulri]

I am seeing TBN used, and I am wondering how to interpret these numbers. I realize that as more miles pile on, the number goes down.

But what does a low TBN mean? Does it mean the oil is still neutralizing acids just as well as it always had, but that it won't be able to do it for much longer? Or does a low TBN mean that the ability to neutralize acids has decreased?

 

[53' Stude]

I believe that as the additive package does its job, yes the TBN will decrease. This is normal also and a oils color is no indication of bad things.

 

[paulri]

Originally Posted By: car51
I believe that as the additive package does its job, yes the TBN will decrease.


And as the TBN decreases, does this mean that the ability to neutralize acids decreases also, or does it mean only that the length of time that the oil can effectively neutralize acids, is decreasing?

 

[Donald]

Keep in mind you are likely to get a slightly different TBN if you sent the same oil to different labs.

TBN is only for the additive package. You need oxidation to see how the base oil is holding up.

 

[sicko]

Let me preface this by saying, I don't know the answer to your question. What follows is just my guess, chances are someone who knows more than me will come on here and give a more educated answer that might conflict with what I said.

I believe that when the TBN is getting low, its ability to neutralize acid decreases. I say this because you can get a TAN (Total Acid Number) with your UOA, and if I recall correctly, the TAN stays low while the TBN is high, but is very slowly working its way up. After the TBN gets low, the TAN starts rising faster. So even though the TBN is still there (just low), the TAN starts increasing.

Again, that's just my thoughts/guess on the matter, but I've never studied it and could easily be wrong.

 

[userfriendly]

I'll go with "B".....
1. A low TBN means that the ability to neutralize acids is decreased.
2. Once the TBN is reduced to 70% of it's original value, it is no longer functioning at design performance.

 

[Kuato]

Discussed in depth on some threads, I know the search function rots on here so I'll give it a shot. Once TAN gets higher than TBN, the oil begins to thicken, which will eventually form deposits and sludge. Jury is out on exactly when it reaches this critical stage. However there are UOAs on here with TAN somewhere around 5 and TBN around 1.5 and the oil is otherwise fine.

edit: Oh, and TBN depletion is NOT linear, it depletes quickly at first then slows dramatically as the miles go on.

 

[Pontual]

Wouldn't a base (alcalinity) always fight acids, kind of imediately? If too much acid formation, wouldn't deplete TBN quickly or almost imediatelly?

 

[m37charlie]

The bases in motor oil that comprise detergents and result in TBN are called weak bases; when reacted with sulfuric or nitric acids they form weak acids.
This is called a buffered system. In such the pH stays nearly constant until almost all the base is used up.
Ever do the titration of Na acetate with HCl, or acetic acid with NaOH in high school chemistry?

Charlie

 

[userfriendly]

Back in the day we used to clean the top of batteries with baking soda and water.
Some would argue that water is good enough and rile the old timers.
"I've been doing it this way 20 years before you were in diapers kid, and I ain't changing now to keep your science teacher happy".

 

[weasley]

Have a read of this.

 

[dustyroads]

Originally Posted By: weasley
Have a read of this.


Thanks weasley...excellent refresher course! You always put up good info.

 

[paulri]

From an article here, Engine Oil Analysis:


TBN
The TBN (Total Base Number) is a lubricant’s reserve alkalinity measured in milligrams of potassium hydroxide, or calcium sulfonate per gram of oil. In more simple terms it is the amount of active additives remaining. This number is important because combustion byproducts tend to form acidic compounds and the TBN is the acid-neutralizing capacity of the lubricant. The TBN does not decrease linearly with the time it has been in use. Example: it could start out at a TBN of 10, drop to 5 after only 1,000 miles of use, and then stabilize around 3 for a majority of the remaining service life. A TBN of span>

This section here says nothing about how oil with a low TBN can't neutralize acids as well--it suggest that it won't be able to do so much longer: "a near depletion of additives." But it said nothing bad about the service life of the oil that had a TBN of 3,from an original 10. Of course, I am reading between the lines....