I have a 6.7 in my 2008 ram 2500, I used to get 20/22 mpg hwy mileage.It's got approx. 47000 miles the fuel mileage has dropped from 20/22 mpg hwy. to 13/15 mpg. No significant problems runs good no modifications cannot figure out. Speed does not matter, 55 mph or 70mph still poor mileage. Any suggestions.

 

Going by the overhead console? All stock?

 

assume no deletes?

winter fuel can have that affect, but also a caked up DPF can as well. Try running your truck hard up some hills loaded down with weight or a heavy trailer and really try to push the truck hard up the hill. That should get your EGTs up high enough to burn off excess soot caught in the DPF and VGT.

Try that, and if it does not work we can dig deeper. usually the largest economy issues with the 6.7L are related to the DPF though. (the reason most people delete them)

also any trouble codes in the computer?

 

Even with the deletes and hypermiling, I wasn't ever able to get over 20 mpg in my 08. My best overhead reading was 24, but it actually only hit 18.

When I bought it the overhead display showed an average of 10.

 

gearing and area you live in makes a big difference too....most of the high mileage guys live in very level areas and drive 50-55 tops to achieve great mileage...faster you go past 50-55 the less mileage you get because of increased wind resistance.

 

Yeah, my attempt at good fuel economy was in FL from Orlando to Sarasota, when I lived down there. I was doing ~70-75 though.

 

With my 3500 Dually I get only 17 on Hwy if only absolutely flat and doing under 65 ml/hr. When towing 5000 lb it drops to 12.6 on hwy
My combined though is 12.8 now. Truck has only 2000 miles. I don't know if it will get better or not.

 

Yikes. That's low for that light of a load. I *averaged* about 12.5-12.8 over about 4800 miles while towing a 24' car hauler with a combined weight over 20k.

 

what is the most economical speed?

 

20k - that's bumper pull or 5th wheel?