Would like to hear this too. I have a good 1655 diesel with 300 hours on a rebuild. Runs good and I have been using Rotella 15w-40. Oil pressure is a little slower to build on cold starts than I would like
I heard they reduced their ZDDP content in this oil and that it will ruin flat tappet valves. They say the synthetic rotella t6 5-40 is a better alternative. Im thinking about switching, but havent decided for sure. Not sure 5-40 is thick enough for an older engine, but that does seem to be the trend.