Currently using Pennzoil YB 5w-20 with a 4000 OCI on 2007 Jeep 3.7. Plan i keeping the vehicle for a long while and was wondering if it would be worth it/extend life of engine at all if I switched to the Napa Synthetic. Or is it a total waste....I realize i could extend my OCI's but any other difference in engine life? Hard to beat the $12/13 I pay for the YB. But the NAPA ad caught my eye and they seem to have it on sale every few months.