I recently got my first diesel: 5.9L, 4X4, 6 speed man., 140K miles, flatbed with lift kit, trailer brake, & exhaust brake. I am getting only 13.7mpg & thought I should be at 18-20mpg.
I changed oil & filter, air & fuel filter.
Do I need to take it to a garage for diagnostics,? Any help is greatly appreciated.
DBP

 

There are many variables that affect MPG.
What year model truck?
What rear end?
Is the 13.7 hand calculated or from the overhead?
Is that while towing or not towing?
What kind of terrain, e.g. flat or hills?
What speed?
In town or hwy?

 

What size lift/tires?
Flat terrain/Hills/Mountain passes?
Into the wind?

I tend to be on the high-end of fuel economy with my 2006 when I compare it to the bulk of threads listing FE. Before my lift I averaged 17.6mpg commuting, I would frequently get 18.5-19.0 on long trips (SF to LA or SF to Tahoe/Reno). With my lift I now average around 15.5mpg commuting. I haven't taken a long trip yet to determine that aspect of mpg, but I'd assume it'd be 17 or so. In 7 years and 90K miles I've hit 20mpg's twice, once was 20.6mpg sandwiched between rigs traveling 55-60mph down I-5. All hand-calc.

 

What type of flat bed? Most will hurt mileage because the way they stick out to the side and are very squared off = more drag.

The lift and tires will also kill mileage. Creates more drag underneath and added rolling resistance from tires.

 

My 2005 4 door shortbed 3.73 2wd auto got 21mpg running 65mph this winter. I am gonna go on a long haul interstate trip in June and am curious to see what 75mph and 70mph will do for MPG and summer grade fuel. I have only had my truck for about 8 months and havent traveled much in it yet.


47

 

This is a 2004 Ram 2500 4X4 not a duelie. The flat bed is a big CM about 6'8"X8'6" with tool boxws under. The tires are Pinnacle Grizzly Grip 285/70/17 (not exactly road tires. I do not know the rear end gear ratio but wonder if it is a 4-10 or 4-11, The tach runs about 2400 at 75mph. The mpg was hand calculated over two 600 mile highway trips, Cheyenne to Topeka (downhill) and Topeka to Lexington KY by dividing gallons into miles traveled.

 

Do you know if the speedo has been calibrated or are you factoring in the tire size difference? You're traveling further than your odometer is saying if not corrected. If you're not sure, borrow a GPS if you don't have one and compare the speed to your speedometer.

I haven't corrected mine and when I'm going 65MPH per speedometer, my GPS shows 71MPH.

That's 2 things counting against you...Faster than advertised and further than advertised.

Here's an example for your situation...

Your odometer is off by .0337

600mi. X .0337 = 20.22mi., not much it seems but that would equal .5mpg over a 40 gallons.