2008 Pontiac Grand Prix, 3.8L ("the 3800") non-supercharged, 170,148 miles on car Out: Mix of Castrol Conventional and Mobil Super HM 10w-30, Purolator PL10111 Oil filter In: 4.5 Quarts Delo XLE 400 10w-30 Synthetic Blend (CK-4/SN), ACDelco PF47E The Series III 3800 is spec'ed for 5w-30, but I like running 10w-30 (spec for Series II) during the warmer months. This car consumes about 1 quart every 1,000 miles (bad piston rings). Other than the oil consumption, the car is great. I'm sure there will be little to no difference in consumption, but for [censored] and giggles I decided to throw in diesel oil which I found on sale and also happened to be dual rated CK-4/SN. I plan on leaving this fill in until November/early December, which will probably be somewhere around 7k-10k miles. Any input appreciated.