I don't want to start a big brew-ha-ha about TBNs, but I would say that he can definitely run that oil longer, without even knowing what the TBN is. We largely base our recommendations on how much metal is in the oil. An engine that produces a lot of metal but still has a high TBN--I'd say don't run it longer. The metal makes the oil too abrasive. But an engine that produces very little metal (like this one) and has a low TBN, I'd tell him to go ahead and run it longer.

It's worth noting that the TBN doesn't drop in a straight line. They follow a curve. Most gas engine TBNs will start out around 8 or 9, diesels at 11 or 12. They tend to drop quickly at first, then they level out a bit and drop much more slowly. The TBN level will also depend on how the driver uses the engine (racing? got a lead foot?) and the conditions you're driving in (desert? frigid cold?).

You don't have to have a TBN for us to give you a recommendation on whether or not you can run the oil longer. If the oil isn't doing its job, it will show up in the analysis in other ways (high wear, poor physical condition of the oil). So I say, the engine looks great. Run a longer oil change next time!

Kristin Huff
Blackstone Labs