bad mpg what to do?

I drive a 2007 that's basically the same as yours. Raising rpm will only make your mpg worse. I cruise at 1300 to 1400 rpm which usually translates to 62 to 64 mph. Running moderately sized loads I'll get around 5.8 mpg, with heavy loads,especially in the mts it will drop to around 4.8. I also try not to wind it up past 1500 when accelerating. I've been told by a mechanic I trust that the only way to raise mpg in older high mileage trucks is to install new injectors ( about 2500 plus labor). I'm going to try adding some top oil to my fuel and see if that will help a bit because I believe any Detroit should get at least 6.5 under moderate loads.

 

my t600/mbn gets 5.1. Best I had is 5.7. Planning to put muffler and reflash.

 

Be aware that you are also dealing with winter blend diesel. I have a 2014 Volvo 780 that normally gets between 7 to 8 mpg during the warmer months, but that fuel mileage declines in the colder months due to the winter blend and cooler engine temperatures. I wouldn't change the horse power just yet, but would take the governor off. It also depends on where you just ran that load from and to. If you were driving west on I-80 which is a gradual up hill climb between Nebraska and Utah, mileage will go down. If you are along I-10 between El Paso, TX and CA, you should get better mileage. Most important you can't just the fuel mileage on a new truck based on one load. Take a month, watch what kind of loads you pull and the terrain. Play around with your speed also. My truck gets the best mpg at 70 mph, but a Detroit 60 may do better at 60 or 65 mph. You can also go to myfuelgauge.com and see what other drivers are getting with similar truck and engine.

 

So did the OP take it to folks that actually know these engines inside and out then? Or still trying the quick fixes that rarely if ever work?
I get just under 5mpg at @100k lbs on various terrain, mountains, etc, so it is indeed low in my book. I would love to see someone shifting a Detroit S60 under 1500rpm's when at 100k lbs too for that matter....

Martin

 

I think this is the best word of advice on the thread. And comments about winter blend fuel are also relevant. First things first make sure everything is as it should be. No boost leaks, no dirty filters, overhead adjustment has been set.... the small ordinary things that can be the cause of poor mpg's. Maybe poor driver habits need to be adjusted. Then and only then give an ECM flash a try. Because the best most efficient ECM tune known to man will still net poor mpg's if routine maintenance on other things are ignored and the driver has poor habits.

 

Im only complaining about the turbo, ecm, muffler, and the camshaft on mbn.