[cnavarro]

Sorry Paul, not trying to single you out. Just I get a lot of phone calls re: M1.

Most definitely Paul, your results showed that the 2 yr, 12,000 mi drain interval is certainly doable. I just had another sample of Pentosin 5w40 with 2 years and 7,000 mi still had a TBN of 7.2 (started at 10), with wear levels the lowest I've ever seen from an M96 engine (5w40, SL rated). Driving styles and habits clearly affect drain intervals, no argument there.

I myself have observed a 5,000 mi interval (with changes approximately every 6 months) gets me to a TBN of just under 5, which to some, is the sweet spot of when to change your oil. That's with mixed driving including short drives where the oil isn't given a chance to get hot enough to vapor off the water content. Winter driving also seems to reduce TBN faster and yield increased wear levels. Cars that aren't driven in the winter aren't subjected to the demands placed on the lubricant that otherwise a year round car might see.

Also, forgot to add, oil formulation has a great deal to do with drain interval too. Oils with less Zn and P will form less acid, allowing longer drain intervals. Secondly, the majority of oils, M1 included, use primarily a Ca-based detergent, that is more thermally stable and maintains TBN better, allowing for further longer drain intervals. A lot of the oils I personally like, due to formulation, would require shorter drain intervals accordingly. Good example of how this affects drain interval is Valvoline NSL Racing - they recommend a 600 mi drain interval on a 5 qt capacity, which I've verified through UOA, adjusting drain interval for increased volume.