I don't really see how anybody can justify spending the money on synthetics in a diesel. You get so much soot in the oil you have to change it more frequently than you would in a gasser, so you can't really do the extended oil changes. I change mine every 3000 miles or three months which ever comes first. I do top off with synthetics though. It helps keep things a little cleaner in the engine and makes up for any lubricating abilities lost by the dino oil.