Why high TBN and TBN/TAN crossover don't matter much. Throw this in with the 4-ball wear test. Marketing.
From Weasley:
"I'd hazard a guess that many BITOGers who think they know what TBN is, probably know only the basics and possibly not enough to actually know how to interpret VOA/UOAs.
TBN is not TBN. Yes, yes, we all know that it is the measure of an oil's alkaline reserve, which is used to neutralise acids and protect the engine. But there are various sources of TBN, and it isn't all freely available to do acid neutralisation.
TBN typically comes from:
1) Detergents
In fact the TBN contribution of detergents is, itself, in two parts. There's the natural TBN of the detergent molecule itself, typically quite low (up to around 25 mgKOH/g). But there's also the main TBN contributor, the so-called "overbasing". This is typically calcium carbonate which is 'dispersed' throughout the detergents as "micelles". Since CaCO3 is not oil-soluble, it has to be carried around in the oil by the detergents molecules. Overbased detergents are in the region 200-400 mgKOH/g.
2) Dispersants
Dispersants, dependent on their type, can contribute a reasonable level of TBN. However this TBN is "ashless", in other words no metal salts but all from organic molecules. This kind of TBN is not as ready to neutralise acids as the overbasing above.
3) Antioxidants
These are used in small amounts, but can have high individual TBNs. Again they are ashless and not highly neutralising.
Furthermore, some types of TBN react only with stronger acids (mineral acids derived from combustion of sulphur and nitrogen compounds in air) and not with weaker ones (organic acids derived from oxidation of the base oil and other components). So the type of TBN is as important as the amount.
Next there's how to measure it. There are several TBN measuring techniques. The typically-used one in motor oil is by potentiometric titration, almost always by automatic titrators. However, the specific methods used to get a TBN number differ depending on the material you are testing.
Here's the rub: fresh/virgin oil TBN is measured by ASTM D2896, which is quite an aggressive method that titrates almost all of the alkaline material, thus giving a relatively high result. However, used oil TBN is almost always done by ASTM D4739, which is less aggressive and doesn't titrate all alkaline materials, particularly the less-reactive stuff. If you run these two TBN methods on the same sample of oil, you will get two different results - which one is right?
In order to make a meaningful conclusion you need to use the same method for all samples, so you need to make sure you get a VOA at the start of your oil monitoring period, and not just rely on a technical data sheet for the start point.
You also have to realise that there may be some TBN you will never 'get at', so a residual TBN may always show up in a used oil, regardless of how used it is.
Finally, a particular bug-bear of mine, is this notion that TAN/TBN crossover is a reliable end point. TAN and TBN numbers are not linked on a see-saw and the numbers from the tests are almost arbitrary. There's no magical 'switch' from good to bad at this cross-over point; the oil doesn't suddenly change from being alkaline to acidic. It is, for sure, a handy and easy-to-explain point which, in the absence of any other data, may as well be used, but you have to take an holistic approach to UOA and look at factors like wear metals and viscosity to see whether the oil's TBN reserve is exhausted.
So, back to the original question - since TBN is not any kind of proxy for quality or performance, there's no benefit to putting it on the label. Total performance of the oil is conveyed in the performance specifications (API, ACEA, OEM etc)."
From Weasley:
"I'd hazard a guess that many BITOGers who think they know what TBN is, probably know only the basics and possibly not enough to actually know how to interpret VOA/UOAs.
TBN is not TBN. Yes, yes, we all know that it is the measure of an oil's alkaline reserve, which is used to neutralise acids and protect the engine. But there are various sources of TBN, and it isn't all freely available to do acid neutralisation.
TBN typically comes from:
1) Detergents
In fact the TBN contribution of detergents is, itself, in two parts. There's the natural TBN of the detergent molecule itself, typically quite low (up to around 25 mgKOH/g). But there's also the main TBN contributor, the so-called "overbasing". This is typically calcium carbonate which is 'dispersed' throughout the detergents as "micelles". Since CaCO3 is not oil-soluble, it has to be carried around in the oil by the detergents molecules. Overbased detergents are in the region 200-400 mgKOH/g.
2) Dispersants
Dispersants, dependent on their type, can contribute a reasonable level of TBN. However this TBN is "ashless", in other words no metal salts but all from organic molecules. This kind of TBN is not as ready to neutralise acids as the overbasing above.
3) Antioxidants
These are used in small amounts, but can have high individual TBNs. Again they are ashless and not highly neutralising.
Furthermore, some types of TBN react only with stronger acids (mineral acids derived from combustion of sulphur and nitrogen compounds in air) and not with weaker ones (organic acids derived from oxidation of the base oil and other components). So the type of TBN is as important as the amount.
Next there's how to measure it. There are several TBN measuring techniques. The typically-used one in motor oil is by potentiometric titration, almost always by automatic titrators. However, the specific methods used to get a TBN number differ depending on the material you are testing.
Here's the rub: fresh/virgin oil TBN is measured by ASTM D2896, which is quite an aggressive method that titrates almost all of the alkaline material, thus giving a relatively high result. However, used oil TBN is almost always done by ASTM D4739, which is less aggressive and doesn't titrate all alkaline materials, particularly the less-reactive stuff. If you run these two TBN methods on the same sample of oil, you will get two different results - which one is right?
In order to make a meaningful conclusion you need to use the same method for all samples, so you need to make sure you get a VOA at the start of your oil monitoring period, and not just rely on a technical data sheet for the start point.
You also have to realise that there may be some TBN you will never 'get at', so a residual TBN may always show up in a used oil, regardless of how used it is.
Finally, a particular bug-bear of mine, is this notion that TAN/TBN crossover is a reliable end point. TAN and TBN numbers are not linked on a see-saw and the numbers from the tests are almost arbitrary. There's no magical 'switch' from good to bad at this cross-over point; the oil doesn't suddenly change from being alkaline to acidic. It is, for sure, a handy and easy-to-explain point which, in the absence of any other data, may as well be used, but you have to take an holistic approach to UOA and look at factors like wear metals and viscosity to see whether the oil's TBN reserve is exhausted.
So, back to the original question - since TBN is not any kind of proxy for quality or performance, there's no benefit to putting it on the label. Total performance of the oil is conveyed in the performance specifications (API, ACEA, OEM etc)."
