How much emphasis should be placed on a higher TBN oil for a 10,000 mile drain interval ? I traditionally go for tbn's of around 9 and above etc when choosing an oil. Some oils that have the same oil ratings may only have a tbn of 7 etc. Does this mean less additives or different additives ? For example, most SL/SM CI4 are 9 and above, yet some only have 7 and so on.