I use 5w-30 syntec in all my gas engines,52 8BA,305 sbc,06 and 08 cars,portable generator,power washer,Wright Stander mower,Sears push mower. Wife buys the 5 quart jugs when on sale and I dont worry about different grades for different engines. Change oil about once a year(06,08 cars at 10000 miles,8BA around 3-4 thousand miles,305 around 5-6 thousand miles) Pete537 people have read this post, I wonder if any one of them are using synthetic oil in their Flatherds????