Ive ran alot more differnet oils in Jeep 4.0s(have 5 Cherokees with the 4.0 right now), Moms 2001 XJ has 4.0 i take care of as does Girlfriends 2003 WJ, that currently burns the Castrol EDGE 10w-30 its filled with. I can say that if Your 4.0 is in good mechanical shape, a 10w-30 is ideal, and what Crysler recommended from the factory, not 5w-30. Not that 5w-30 is bad for the 4.0, in sub 20 degree temps, i think the 4.0 prefers a 5w-30, but above freezing, I use 10w-30. Plain old, current PYB (conventional Pennzoil) in a 10w-30 weight is hard to beat, maby one of the best oils for the Jeep 4.0(my 87 XJs 298,421 mile 1st year 4.0 was run on PYB until i bought it at 269,??? miles, and still very strong and smooth, no ticks, oil burning, just a little rear main seepage) its just so plain jane for me.