10w30 for ISX?

I would tend to agree. While the silly 15,000 mile interval that Detroit recommends for my pre-EGR 60 is pretty lame, the reverse is also true. Some 50K oil change interval makes for interesting marketing, and may indeed be possible in some situations, but I am in the camp that intervals should be backed up with sound used oil analysis to confirm anything. And just a simple read on one used oil sample is not sufficient. You have to track samples over time and get a idea of how the oil trend line is developing. How are the wear metals correlating to one another and in relation to oxidation, nitration, and TBN depletion. One should do the initial oil change early anyway, and from that point on, start tracking oil samples and see where the best oil change interval is.

For instance, the difference between the 15K Detroit recommended interval on my pre-EGR 12.7 60 and 20K, there is no appreciable difference in oil quality. Wear metals are still just on a steady upward trend. TBN is slowly depleting at a steady rate and oxidation and nitration are still fine. Up to 25K on my motor, the trend stays steady, but at around 25K, I start getting readings on different aspects of the oil sample that shows some "spiking" of the trend lines in relation to each other. So that is the limit I place on doing an oil change. I don't change oil till I reach 20,000 miles / 400 hrs, and I don't go beyond 25,000 miles / 500 hrs.

Each engine and oil combination is different. There is no one size fits all best interval. If you are serious about your motor, then you have to use a healthy dose of common sense along with some test results and come to the best solution for your situation. If 35K shows to be a good interval, then go with it. If you can pull off 50K and have nice steady trend lines that confirm it, then go for it. But just basing your decisions on feelings or marketing nonsense is not wise. Almost any engine made in the last 20 years, along with the current oils we have and the ULSD fuel we are using, can easily go at least to 20K oil change intervals irregardless of what the OEM may have said in the past with lower quality oils and high sulfur fuel. Since then, CJ-4 oil is the standard, and we all have to use ULSD fuel. Those two things alone have made it so the old 10K oil change is unnecessary. But old habits just won't die, and some people have money burning a hole in their wallet and feel the need to spend it. Instead of spending it on 10K oil changes, why not take the wife or girlfriend out for a nice evening and a movie.

And if you have a stack of used oil samples, like I do, in PDF format on your computer, it makes for some easy confirmation to the next buyer of the truck that you have taken the time to do things right. That can increase your leverage in resale.