'pappy said' every 3000 miles and that's what I'll stick with. I just run it down to the Wal-Mart and by the cheap crap, it won't be in there long. Cost's me about 80 bucks a year to do this and I don't even get dirty, and tie this in with a hair cut and it cuts down on the fuel bill as well. Now if I had a brand spanking new hot rod I'd consider synthetic and change it every 3000 miles, which would be of coarse about once a year, because I wouldn't drive it all over the country. That's what my beater is for. LOL