I run NOTHING but MOBIL 1 or ROTELLA full syn oils!! and not just in my jeep but all 4 of the vehicles i currently own, and every car i've owned since they came out. I switched my jeep to mobil 1 when i bought it (108k miles) and when i took it out to hop the 4.0l up to over 300hp it was the cleanest oilpan and whole motor that i have EVER taken apart (and i've taken a lot of motors apart even with fewer miles that were MUCH dirtier!!! and DO NOT use FRAM filters, they are CRAP!! WIX is the cheapest brand of filter you should EVER use!!! well if you really care about your engine anyway, and the straight 6s are damn near BULLET PROOF, they will run forever if you maintenance them correctly!!