As you likely have found, they come with 10-30 from the factory. That may be fine for winter use, or northern climate's, but down south where 100* day's are common, i drained mine about a month after i bought it. 15-40 went back in, and will soon be dropping it for syn 5w40 now that winter is here, and the truck is closeing on 8k miles.. The service manager at the local dealer claims they go back in with 15-40, any time a customer comes back for an oil change, unless the customer says otherwise. I have allways tried to have atleast 5k miles on an engine before i switched to a syn oil..always used ford 15w40 in my 6.4
are the 6.7's different.
seems lots of people using 5w-40 synthetic ford oil . it is ok to start using the synthetic on first oil change or do you have to wait a few