you can swap synthetic to regular oil every oil change if you wanted....synthetic's best quality, to me, is that it won't burn as easily as regular oil....if you have a turbo (most of them), then it will help extend the life of it by not allowing the oil to cake up on the bearings as easily.....it will cause some turbos to make a lot of odd sounding noise...i don't use it on regular engines...waste of money.....driving habits and maintenance make more of a difference...$4-$5 a quart for it is a little crazy.....if you feel like it's gonna make a difference, then you will feel that difference...do what you want....turbo, yes...NA, no....