I read my Dodge Caravans owners manual, it describes short trips, lots of idling to change at 3k or 3 months, whichever comes first. We drive this van under severe service always and I hit 3 months before I ever hit 3k. With Mobil's claims of extended drain on their oils, is it safe to do so given my van is out of warranty? Do the engineers who designed the engine know more about proper OCI's than the oil companies do? It's not like the manufacturer has anything to gain by having us change oil on shorter oci's anyway. So I want to know what is best given what the manual states.