2004 6.0L f250 w 105K miles. Ive had it for 2 months. When I first got it, it had to go back to the dealer to have the EGR system replaced. When I got it back I was running 17-19 mpg. A few weeks later it was 15ish. Now I am consistently getting 13-14. This is mixed highway and city driving. I have been using ford cetane booster and diesel supplement from advanced auto. When I got the truck back it threw a code for turbo underboost, but I cleared it and it hasnt come back. Ideas?

 

No one knows how you calculated your fuel mileage, or where you live and what type of fuel you are burning. 13-14 is typical average for most 6.0's right now in cold northern states.

 

When was the last oil change?

 

Your mileage will go down when you are running winter blend diesel.

Make sure your MPG is hand calculated. The computer display is commonly referred to as the "lie-o-meter" due to it's inaccuracy.

Fuel mileage is a widely discussed topic on FTE. Use the search feature and you will find lots of reading info on this subject. See the following recent thread as an example.

https://www.ford-trucks.com/forums/1...el-milage.html

 

my lie o meter always reads 11.4 no matter what so I dont ever use that. I go to a truck stop fueling station now, but I was using shell before and getting the same results. I use my trip odometer and do the math based on the amount of gallons it took to fill up from the last time. So 13-14 is average huh? that sucks...a friend of mine has a 05 duramax gets 20-21.

 

Identically equipped with the same load, axle ratio, operating conditions, etc.?

Absolutely no way.


Right now, in extreme cold, I am getting 13-14 all around (including a lot of idling / warm up).

On the highway, with cruising speed down to 50mph and slow starts, I can get 20-22

That is with a E 350 van body (lots more wind resistance), and about 1,000lbs of payload.


Run this test:

Swap trucks with your friend.

Fill it up, and run 2 tanks and see what you actually get given your way of operating.. etc.

Then correct for things like axle ratio, payload, etc.

Report back.

 

Yes I can see -2 MPG with winterized fuel.