I run a service center. I use Pennzoil Syn. I change my oil every 3000-3500 miles. The only real difference in the major brand (Penn., Castrol, Mobil 1, Val)synthetic oil's are minor differences in detergents. I have found a slight increase in fuel mileage, as well as faster preasure on start-up. I find it very funny that some people belive that a synthetic oil(read: man made) is just conventional oil(read: from the ground) with Slick 50. I have always thought that engine additives are not needed if you properly maintain you engine. I doubt Robert Yates or Roger Penske ever poured a jug of Motor Up into a motor that made some noise during a pit stop.
