Join Date: Aug 2010
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My '08 F-350 is as big as it gets, dually, 4x4, long bed, crew cab, 4.10 LS, automatic, gooseneck hitch -- probably 9500 pounds rolling with my family and vacation gear. And I get 17-18 MPG on 100% highway hand calculated trips if I can keep my foot off the accelerator and keep speeds under 65 MPH. Putting around town, it's closer to 12-13 MPG hand-calculated.
1) Don't trust the in-dash MPG measurement. It clearly lies. When it says 15 MPG average for a mixed city-highway tank, my calculator and a consistent fill level shows me 13.
2) Keep speed under 65-67 MPH if you can. These trucks have a huge frontal area, and wind resistance becomes a major obstacle as speed increases. A truck that gets 18 MPG on the open highway at 60 MPH probably gets 13 MPG at 75 MPH. Keep an eye on the turbo boost -- I try to keep my boost under 7 PSI on the highway if I'm trying to stretch the miles on a tank between stops.