I heard a lot of people say that they run Shell Rotella T 15W-40, so that is what I got. The 7.3s take 14 quarts I believe. I went to Wal-Mart because someone said they carried Ford fuel filters. Well, they didn't have the fuel filters, but they had the Rotella oil for about 7.50 a gallon. They do have the Ford oil filter, too. That was $10. So, about $45 to change the oil.