Fuel Mileage on my 325/600 2004 dodge 3500 SRW shortbed Quadcab 4X4 has been depressing. Local driving on the overhead was in the 11's and highway in the 15.5 to 16.5 range. This is without towing. I assumed that since I have the 4.10's and the 4spd auto and a moderate to heavy foot I would be paying the price at the pump . I was considering larger wheels & tires or changing the axle ratios to 3.54 . Each option was about $2500 on Long Island, N.Y. I called up Cummins 1 800 DIESELS and complained about the poor mileage. The phone rep. suggested I visit my dodge dealer to get my ECM reprogrammed with this code TSB 18-037 -04. Viola , I saw the overhead go into the 20-21 range for the first time in over a year . My mileage is 16400. The improvement could also be partially attributed to the weather limiting speed to about 65 mph or 2000rpms. I hope that this is helpful. I do have two questions to the forum. What is the most economical rpm to be at for highway speeds? How much would synthetic oil in the crankcase improve fuel economy ?

 

From what I have found you will start going down in fuel milage when you increase your rpm above 2000. Try to keep it below that for best fuel economy.

Travis

 

make sure you hand calculate. when i put my edge box on mine it sat 22+ when i am getting 18ish

 

What does this mean?

 

That TSB is a ECM flash update that is available for 04.5 600 engines with a specific build number range. I don't think it covers any 2005s unless very early engine builds. It was for white smoke at start up and to improve overhead mpg calculation accuracy. It stated a potential 1 mpg increase in fuel economy was possible. It did not do anything for my mileage when I had it done last year. It just changed the overhead mpg from being 1 mpg low to being 1 mpg high. With my current mods and various box configuration my overhead is about 2.5 mpg high compared to hand calculated.

 

Cool, thanks.