I have a 99 Wrangler with the 2.5L with 34,000 miles. I have been looking over the forum for the better part of the last 2 hours and have seen many of you 4.0 owners are running rotella or some other kind of 5w40. I currently run Mobil 1 10w30 and have since it had 24,000 miles. I was wondering why everyone with a jeep has been putting 5w40 in their jeeps and if I would get anything out of changing my oil weight in my little 4 banger 2.5L? I am sure the owners manual says to run 10w30 and cannot find the benefits of running a 5w40 in any posts. I have also been changing my oil (M1) and filter (K&N) at 3 months or 3,000 miles whichever comes first and outside of this site many in the jeeping community has agreed on that. However, I come on this site and it seems as though everyone says it's ok to run mobil 1 for 5k-10k. I have learned about (UOA) but it is hard to go against everything you have been told for years and years!!. With this short change interval am I just throwing money away?