I have a 2007 2500 and the fuel mileage is usually on average between 19 and 20 miles per gallon, for the last few months it has dropped between 12 and 13 miles per gallon all the filters are new and clean no performance changes any advice or help would be greatly appreciated!

 

These are the calculated mpg numbers, correct? (Not from overhead). Has your use changed? (Average mph changed as calculated from Elapsed Time counter). Past that: brake drag, alignment, tire pressure, etc.

 

The list is long...

- weather changes?
- change tires?
- change where you buy fuel?
- change the trans fluid too, adjust the bands as well?
- add a tool box or brush guard to the truck?
- add a tuner box
- did the dealer do a ECM upgrade?
- any codes?
- change the brand and weight of engine oil?
- how about the AC uit... are you using it now vs before?

lots of things affect the mileage, especially tire pressure (as mentioned already) and wind/weather. You have to think about what has changed since then and go from there.

 

Thanks for all the tips in things to consider but none of the above has changed and that is calculated mileage not from the overhead. Its the same tires ,tuner, driver no ECM changes no tool boxes same southern temperatures all fluids are up to Par engine tranny and diffs I'm stumped don't know where to look next but thanks anyway!

 

Mine did the same think just not as bad. My front breaks were draging just a little and had to replace the calipers. After that it is back to 20 mpg.

 

I assume this means that your engine oil level is normal and has not increased, because if increased that could mean a leaking injector.

 

Is your engine coming up to normal temperature on the guage...

Maybe the thermostat is gone .

 

Forgot: Have you checked the CAC for leaks?