I now have a little over 9,000 miles on my 04 LB7. After about 6k miles the mileage started dropping and dropping fast. I was getting anywhere from 16 mpg to 19 mpg with mixed city and highway driving. It started dropping and finally got to averaging around 14 mpg. I thought the fuel filter might be the problem so I changed it. Ran down the highway last night at 65 - 70 mph with no wind and got 13 mpg.


I am not running any mods and haven't changed the truck any but I did switch oils from Rotella to Delo at about 6k miles.


Any ideas as to why it has worsened so much? The truck still runs great.

are you goin by the dic or doin the math to get your mpg? the Instrement cluster has always be off on mine

on a short wheel base(26 gal tank) i been getting 350 to 380 miles per tank.....

I've been hand calculating and using the DIC and they're usually within 0.1 - 0.2 mpg different. What's worrying me is the drop in mileage. If i never got 16-18mpg it would be no big deal.

Could be the fuel filter.

Air filter? Plugged filters cause the engine to starve for air. I don't trust the sensor, just pull it and look

My range is bang on with rickles04. I'm averaging about 17 mpg and am always running about 9000 lbs.

Step 1: Remove foot from floor with pedal under it.


Step 2: Watch fuel mileage increase again.


Step 3: Smile that fuel mileage increased.


Step 4: Frown cause you are going so slow now.


Step 5: Say screw it, push pedal to floor, deal with mileage and smile again......http://www.dieselplace.com/forum/smileys/HiHi.gif

I notice that my mileage drops off in the winter due to the fuel remix that stations do to prevent gelling, maybe you got a bad batch of fuel. I would also check all of the above.


JP