TBN vs. Wear Numbers

[Phishin]

Most people on BITOG tend to use the TBN of their used oil analysis to set their OCI. Cool, I understand that.

Here is what I don't understand.....

1.) Most people claim that the TBN is an indication of how much active additives are left in the oil. What is the correlation between TBN and additives? I understand that the TBN on any given oil sample might indicate the levels of oxidation or other break downs happening in the hydrocarbon chains...but how can the TBN indicate how much useful additives are left in the oil?

2.) Let's say I run Valvoline 5w30 conventional in my Nissan Altima. At 5k miles, I do a used oil analysis. TBN is 1.0. Wear numbers look good. At 7k, TBN is 0.8 and the wear numbers a up abot 40% from the used oil analysis at 5k miles, but I also drove it 40% more miles. So no acceleration in wear. I keep the oil in and go to 10k miles, the TBN 0.0 and the wears are double that from the 5k miles used oil analysis. But I also drove twice the miles.

And let's just say hypothetically, I drove the car another 10k miles on Valvoline conventional....that's 20k miles on this oil....and the TBN is still 0.0, but the numbers are 4x that of the 5k mile used oil analysis and 2x that from the 10k used oil analysis.

Everyone here would say I should have changed the oil at 5k miles....yet the amount of wear per mile never changed.

Why do people go by TBN and not when they see increases in wear, which would indicate that the oil's functional efficiacy is actually starting to decline?

 

[Astro14]

Because the bases (measured by TBN) are what prevents the formation of sludge (when acids and moisture are present, the oil is broken down). The wear number would indicate when the oil itself has broken down - but that's short term performance parameter. More important is keeping the engine from getting sludged up (and plugging oil passages, destroying parts) for the long term performance of the engine.

You might be able to go 20K on dino...and never see the wear numbers go up...but the fouling of the engine would preclude it ever seeing another 20K after that...

By the way, your hypothetical numbers are off, if the TBN was 1.0 at 5K - it might be way below 0.8 at 7K...many oils start out in the 8 - 10 range...so it can decline more quickly, based on operating conditions...but the point is the same...

Please don't go pouring calcium hydroxide in your oil to add TBN... I am no tribologist...the chemistry is more complex than that...

 

[skyship]

If you Google TBN & TAN it will give you a lot of info on what they are. You are correct to say that the wear metals indicate the end result, BUT there are other important factors to consider other than the wear metals and the big one is SLUDGE formation. TBN is not the best way to figure out if an engine is forming sludge or varnish, but in general terms if the number is comfortably above 1 (I use 3 for severe service or 2 for normal), the risk that you are going to be subject to long terms sludge or varnish trouble is close to nil for a modern engine, because the detergents will still be active. Top up oil also makes a big difference and this can confuse OCI extension calculations. TBN is used because it is not too expensive a test, but oxidation, TAN and other tests can give a better idea of the remaining additives and if they are working correctly.

 

[gfh77665]

Originally Posted By: Phishin

And let's just say hypothetically, I drove the car another 10k miles on Valvoline conventional....that's 20k miles on this oil....and the TBN is still 0.0, but the numbers are 4x that of the 5k mile UOA and 2x that from the 10k UOA.

Everyone here would say I should have changed the oil at 5k miles....yet the amount of wear per mile never changed.


You need to try to understand the difference between RATE of wear and AMOUNT of wear. To put it in simple terms, lets say its pretty cool one day, 30 degrees. Then a warm front passes through and it goes up to 60 degrees. If it did again, do you expect 120 degrees? Then 240 degrees?

The "rate" (doubling) would be the same, but the "amount" of increase would quickly have you in very hot water! See the difference? I would not want 4X the times of wear on my car due to old oil.

 

[TallPaul]

In support of point 1, I just got my used oil analysis back showing TBN 0.6 with tons of active additive left (P of 1300, z of 1400).

 

[skyship]

Originally Posted By: Astro14
Because the bases (measured by TBN) are what prevents the formation of sludge (when acids and moisture are present, the oil is broken down). The wear number would indicate when the oil itself has broken down - but that's short term performance parameter. More important is keeping the engine from getting sludged up (and plugging oil passages, destroying parts) for the long term performance of the engine.

You might be able to go 20K on dino...and never see the wear numbers go up...but the fouling of the engine would preclude it ever seeing another 20K after that...

By the way, your hypothetical numbers are off, if the TBN was 1.0 at 5K - it might be way below 0.8 at 7K...many oils start out in the 8 - 10 range...so it can decline more quickly, based on operating conditions...but the point is the same...

Please don't go pouring calcium hydroxide in your oil to add TBN... I am no tribologist...the chemistry is more complex than that...


One point though about conventional or part synthetic oils is that they don't cause sludge unless the additives have failed, although they can suffer from extended OCI high temp shearing more easily in some turbo cars, the UOA will show that up, so don't be put off conventional oils as the good quality major brand ones don't cause sludge if you don't use them for too long. I know quite a few long OCI turbo diesel chaps that just use cheap conventional oils that contain a lot of Calcium based detergents. They start with a 10/40 and finish up with 15/30 at the end of the OCI, but as both numbers are within limits for their engines their UOA results are good.
If they used Iffy lube conventional with an orange can of death in their diesels they would have real trouble with sludge due to lack of detergents.

 

[Donald]

Some engine companies have published what they considered contaminated oil, as in iron, silicon and TBN. Once any one is exceeded the oil should be changed.

 

[Corvette Owner]

Be aware that "wear numbers" in a used oil analysis don't tell the entire story, actually they don't necessarily correlate to wear because they don't measure all particle sizes. Here is a quote from a paper on this, "A fact which has recently become more widely understood is that spectrometric oil analysis detection efficiency decreases as the wear particle size increases. Large particles are precisely those particles which are most indicative of an abnormal wear mode. Severe wear modes such as spalling, severe sliding wear and cutting wear generate large particles which may go undetected by spectroscopy. This is true to a greater degree for certain types of spectrometers than others. It is also more important for certain types of machines and engines."

Acidic oil is what caused the time limits (e.g. x,xxx miles or 1 year) in manufacturer's oil change recommendations. However, oil additives/chemistry has improved and modern oils don't turn as acidic like old motor oils did.

 

[skyship]

Originally Posted By: TallPaul
In support of point 1, I just got my used oil analysis back showing TBN 0.6 with tons of active additive left (P of 1300, z of 1400).


It does not matter much what the exact Zinc, Calcium and other additive figures are in a used oil analysis, although it does give you an idea about the type of oil in use. The Calcium figure for example increases as the oil is used. Those additive figures look OK, BUT the oil in use is the wrong viscosity for the job in hand and has sheared down even further. It will have chewed its way through the active Calcium trying to deal with the contamination. The TBN is far too low hence the rise in Copper and other wear metals, although the Iron is OK.
The oil used has a lot of Moly, but it does not always help, so looking at the interesting used oil analysis I would recommend cutting the used oil analysis to 5K miles initially with a major brand 5w40 and seeing what the TBN does. At a guess 7500 miles with conventional and 10K miles with an expensive full synthetic 5w30 or 5w40.

 

[skyship]

Originally Posted By: Donald
Some engine companies have published what they considered contaminated oil, as in iron, silicon and TBN. Once any one is exceeded the oil should be changed.


Makes a lot of sense, as Iron tracks miles run, Silicon is bad news for future wear and low TBN means the oil is about to throw the towel in.
I suppose Lead just means it's an old engine in some ways.

 

[volk06]

Originally Posted By: skyship
Originally Posted By: TallPaul
In support of point 1, I just got my used oil analysis back showing TBN 0.6 with tons of active additive left (P of 1300, z of 1400).


It does not matter much what the exact Zinc, Calcium and other additive figures are in a used oil analysis, although it does give you an idea about the type of oil in use. The Calcium figure for example increases as the oil is used. Those additive figures look OK, BUT the oil in use is the wrong viscosity for the job in hand and has sheared down even further. It will have chewed its way through the active Calcium trying to deal with the contamination. The TBN is far too low hence the rise in Copper and other wear metals, although the Iron is OK.
The oil used has a lot of Moly, but it does not always help, so looking at the interesting used oil analysis I would recommend cutting the used oil analysis to 5K miles initially with a major brand 5w40 and seeing what the TBN does. At a guess 7500 miles with conventional and 10K miles with an expensive full synthetic 5w30 or 5w40.


How does the calcium number increase during use???

 

[heynow]

Originally Posted By: gfh77665
Originally Posted By: Phishin

And let's just say hypothetically, I drove the car another 10k miles on Valvoline conventional....that's 20k miles on this oil....and the TBN is still 0.0, but the numbers are 4x that of the 5k mile UOA and 2x that from the 10k UOA.

Everyone here would say I should have changed the oil at 5k miles....yet the amount of wear per mile never changed.


You need to try to understand the difference between RATE of wear and AMOUNT of wear. To put it in simple terms, lets say its pretty cool one day, 30 degrees. Then a warm front passes through and it goes up to 60 degrees. If it did again, do you expect 120 degrees? Then 240 degrees?

The "rate" (doubling) would be the same, but the "amount" of increase would quickly have you in very hot water! See the difference? I would not want 4X the times of wear on my car due to old oil.


Your example has no application in this situation (and I'm not even sure what your point is).

He's saying that if a 5kmi UOI shows Fe of 5ppm, and a 20kmi UOI shows FE of 20ppm, you have the same amount of wear/mile. So changing the oil early would not prevent any wear, as far as Fe is concerned.

 

[gfh77665]

If you cannot understand the difference between "rate" and "amount", then I am sure you cannot understand it at all.

 

[ARCOgraphite]

Originally Posted By: TallPaul
In support of point 1, I just got my used oil analysis back showing TBN 0.6 with tons of active additive left (P of 1300, z of 1400).
Be carefull, they(EP) may not be active, but instead, converted after use but still in the oil in an inactive state. If you drive a car very hard the Z___P will get used up and converted pretty quick (in a couple K miles or faster for hard track use) and not be there for you.

 

[skyship]

I should have said IF the oil volume decrases. I think it stays near the original VOA figure if no oil is used, but that does not mean the Calcium compounds are working, it has no real connection and is more of an indicator of what was in the oil fill. My own goes from 2600 to 2750 over 10K km, the TBN drops from 10 to 5, so all is well.

 

[volk06]

Originally Posted By: skyship
I should have said if the oil volume decrases. I think it stays near the original VOA figure if no oil is used, but that does not mean the Calcium compounds are working, it has no real connection and is more of an indicator of what was in the oil fill.
Mass spectrometers count elements not active compounds. If an additive forms a gas when used it will result in a falling element number, but the residual Calcium compounds that result after it has been chewed up finish up staying in the oil. If part of the oils base evaporates it will cause a slight rise in the number. My own VOA Ca starts at 2600 and finishes up after 10K at 2750 in the UOA. The TBN starts at 10 and finishes at 5, so all is well, but without having checked the oil could have turned into an acid.
Thats my rather rough understanding of the use of the Calcium figure, in other words it's not of much use in figuring out if you have active detergent left.


Right. The Calcium number will still be there even if the TBN is 0. The TBN is 0 because of the TAN and acids in the oil. Like a chemical reaction, the elements are still there but in a different form.

Calcium is the most commonly used detergent in high doses, magnesium is starting to make a come back into oils again because it helps TBN retention.

 

[bigjl]

One interesting thing I have noted is that a lot of the mid to low saps oil seem to have TBN less than 10 sometimes less than 8 when "virgin".

But these same oils are also used over long OCI, for example my Pathfinder has an 18,000mile OCI, though I am changing much less than that too be honest as I am of the opinion that oil and a filter is less than a camchain, turbo or crankshaft.

And there is a strange satisfaction knowing that if just short of you normal OCI you could undergo a 1000mile emergency journey with no issues.

I am sure there is a reason for the low TBN's I have mentioned above.

 

[Astro14]

Originally Posted By: TallPaul
In support of point 1, I just got my used oil analysis back showing TBN 0.6 with tons of active additive left (P of 1300, z of 1400).


That's not active additive. Those are only elements that made up those additives. The chromatograph/spectrometer simply shows elements, not the complex chemicals that make up detergents and dispersants...when the TBN falls that low, it's because those chemical additives have changed by absorbing/converting the acids and dirt...now, they're no longer active, they're almost all transformed and used up...

Active additives don't last for ever...they get used up and change into other substances...sure, the elements are still there...but not in their original chemical form...

 

[TallPaul]

Originally Posted By: ARCOgraphite
If you drive a car very hard the Z___P will get used up and converted pretty quick (in a couple K miles or faster for hard track use) and not be there for you.


I sometimes drive it like this:

 

[Artem]

The OPs example doesn't relate to real life used oil analysis results.

used oil analysis from my 07 Civic EX showed the same wear numbers after 6,800 miles and 12,000 mile used oil analysis, so the 2x the wear after putting on 2x the mileage thinking is severely flawed.

It's still hard to say because with the oil filter getting more efficient with use, the wear could really be increasing some but since the oil filter is catching all the particles, it's not showing up in the used oil analysis report....