I bought my truck early Aug. 10. It is a 6.7L f-350 FX4 CC SRW Lariat w/ 3.31 gears. It used to get 19.4 MPG @ 70. at around 9,000 miles it had fallen to 17.7 MPG. At this point I took it to ford and they could not find anything wrong. I changed out the fuel filters and air filters. I now have 18,000 miles and it is getting 15-16 MPG. I am baffled by this. 85% of my miles are highway and I live in Victoria, TX so I don't think we use winter blend fuel down here. HAs anyone else experienced this or does anyone have any suggestions?

 

I live in Texas and have an F250 FX4 (3.55) that I bought in August as well. My mileage was about 20 and now is down to 16 at best on the highway. My driving habits have not changed. So either it is the winter fuel (which I don't know if it is used here in TX or not) or there is something up with this truck.

 

MY general opinion after having 15 ford diesels is the the trans calibrates itself to your driving style. Over time city mpg could drop naturally. Ive seen this with the 7.3, 6.0, 6.4, and now the 6.7. My f150 behaves the same way. If you run these on the highway a while you ll see it stay better for a tank and start to go down. Im talking hand calculated.