Not sure... they say the TBN is used to measure the amount of active additive left in the oil.
Since I didn't use any additive with the oil...
I guess I was happy with the viscosity rating of 60.9. Since it was between 57-63 it showed that the oil
hadn't broken down or been "overrun" during the 7200 miles, even with the summer heat, and the filter did
a good job with the insolubles. They say "Excessive insolubles can form in oil if the oil is running hot, receiving
more than a normal amount of contamination, is suffering from more (or more severe) heat cycles than
normal, is being run longer than a typical use cycle, or if oil filtration is marginal or ineffective."
I'm waiting for them to send another kit so I can send in the sample I took from the Cherokee...
almost 10000 miles on that oil change.
