Not sure what any of the hard-core oil folks will tell you but 10w40 used to be the standard of what we ran in ALL our rigs for years. The Jeep is the first I've had that called for 10w30, followed by our Subaru which wants 5w30. Jeep is an '05, Sub is '07. With the ZDDP level issues for our engines, I talked with the guys at Royal Purple and they said NOT to add anything to the oil, but instead recommended I switch to 10w40 as it by allowed government specs to have higher ZDDP levels due to weight. They said to switch to 10w40 and not worry about a thing. I did, and have had no issues to date on the current fill, but again, it's been recent and I doubt I have 3000 miles on it yet. I've noticed no difference in running-other than it is a titch quieter, no difference in oil pressure on our dummy guage, no other engine related issues at all. Again, too soon for long term results...
Best of Luck,
Mike
Best of Luck,
Mike