ok... this has been bothering me for a while. i have a 2008 f-250 (gallery) xlt cc 4x4 job 2 with 34000 miles. so here it is... if i set my cruise at 65-67mph on the highway i will get between 17-21 mpg depending on how flat or hilly the roads are. which i think is pretty damn good! but after just 15-20 minutes of in town stop and go driving the milage drops to 12.5-13.5mpg! so i guess what is frustrating me is.. if my truck is doing that great on the highway then how bad does the milage suck in town!!! anyone else having these huge fuel milage differences??

 

yup! Takes alot of fuel to get 8100 of steel moving.

 

Well I average 13.5 on the hwy at 60-65 and 11.3 around town, so I feel your pain... but then again, 4.30 gears and 9300lbs will do that to you... but yeah, if I slow down to 55, get behind a semi that is going that slow (rare), I get 16-17, but as soon as I hit town, 11-11,5 is the best I can hope for.... I have less than 2k miles on it, so maybe when it is broke in (a cpl hundred thousand miles from now) it will do better..

 

Is that hand calc'd mileage or just by what the LOM guage on the dash says? I notice similar results, I'm not sure of the logic in the computer, but I've NEVER actually averaged what the computer tells me the AVG MPG is and also noticed a big drop from highway to city driving.

 

I could speculate there are a few reasons why the mileage goes down in the city.

- no constant speed anymore (kinetic energy converted to heat by the brakes)

- lower EGTs (causes DPF to regenerate, or go into regen more often)

- in the case of only city driving, you have warm up time to deal with. My 6.9 usually averages 13 MPG for short trips of 10 miles or less in the city. The fan clutch itself seems to eat up at least 2 MPG and I was able to get 15 MPGs with the fan removed during the winter.

For highway speeds, I have hand calculated up to 22.5 average @ 70MPH, but there is no flat ground on vancouver island. Peaked as high as 24.9 once.

I agree that 21 MPG is good for a 6.4

 

yea.. thanks guys. glad im not the only one. same thing again today. set the cruise at 67 and it averaged 19mpg for over 20 miles. but within 10 min of town driving the lie o meter shot down to 13.5 and after a day of mixed driving its back to 12.1mpg.... so does this mean my truck is getting 19 on the highway and 7 or 8 in town??