I also have a 460 1997 with 40k miles. Summer, I use either 20w50 or 10w40. . So far no oil usage between changes. Winter trips I use the thinner 10w30, still no usage. I go 3 to 4k between changes. I always check with cold engine. Also tow a Buick Rendevous on tow dolly w/brakes. Don't believe...