Ok, I recently bought a 2000 F-350 CC, LB. I was getting 15.4-15.9 mpg in town, I changed the oil and cleaned the air filter and put some seafoam in the tank, then I noticed a drop in mileage, down to 13.7, so I changed the fuel filter, no change. On the freeway last night averaging 68mph after 20 min of driving it went up to 13.8, then 20 min later 13.9, then topped at 14 even. When I got it 2 weeks ago if I hit more than 1 green light it would go up a tenth, then up another tenth for every green light there after, then down a tenth for every red light I caught, that has stopped, just keeps going lower and lower.I had a small up pipe leak, wasnt affecting boost but I fixed it and no change. What could be causing my bad mileage?

 

How are you calculating your mileage? Sounds like a lie-o-meter...

Only way to get true mileage is fill your tank, drive, Fill your tank, take the miles driven and divide by the amount you just put back in the tank...

 

Dont listen to the lie O Meter it never tell the truth

 

OK, didnt know they were called a lie o meter, will check the fuel mileage the old fashion way from now on, will let you know later, I have the mileage down from when I fueled it last and am going to fuel it today. Does the "KKKmiles left in tank" reading work any better? Thanks