Originally Posted By: Quattro Pete
How is a high TBN achieved? Is it a function of the amount of additives? If so, is it possible that todays oil standards (such as API SM) limit the amount of TBN an oil can have by limiting the amount of additives?
Also, is it possible that some oil bases and add packs can be formulated in a way that despite having a a rather low starting TBN, they will not allow this TBN to drop as quickly?
TBN is mostly achieved through the type and quantity of the detergents. Yes, API SM and other specs do indirectly limit the TBN by the sulphated ash limit since the detergents contain metals (Ca, Mg, Na). Sometimes there are sulfur limits imposed and many but not all detergents contain sulfur.
If the motor oil has awesome everything in it but low starting TBN, that will help it not waste TBN by neutralizing acids that would not otherwise have formed as quickly. But still, it puts the oil at a disadvantage for long drains relative to what it could do with more starting TBN, within reason.