i recently purchased an 04 -f-350 with a 3.73 rear gear and the 5.4 v-8.. ext. cab with 8 foot box.. has a mild at firestone on it.. under the best highway conditions, and not heavily loaded,, what should i expect for the best case mileage on the highway.. i expect it to be noticeably better than the v-10 , and my old truck was a f-250 with the 460v8(very thirsty).. also,, are any of these fuel additives actually worth using as an aid to increase fuel economy? polarisman

 

This has been discussed quite a bit on FTE. Do a quick search and you will find plenty of numbers on the 5.4L. The general consensus is that the v8 and the v10 get similar mpg's. The reason being that these are heavy trucks. The v8 will have to work a little harder than the v10 to get that F350 motivated. I had an '01 F250 SC 4x4 w/3.73's and the 5.4l - it averaged about 10-11 city, 14-15 hwy. My '05 F350 V10 CC 4x4 w/4.10's gets 10 city, 14 hwy consistently.