mmark

Hello..I need help..I have a 2003 Dodge 3500 dually..5,9ltr diesel..I'm hauling RVs from Indiana..so far this month I'm averaging 12 mpg..should be getting better mileage i figure..Open to suggestion..will be switching to Amsoil..soon..Thanks

Spooler

That's about right when towing. Best mileage is obtained at 69mph. Not sure how fast you are going. You probably have the 305/555 engine and it gets the best fuel mileage. What gears do you have?

mmark

Hey Spooler..thanks for the info..it an automatic and the engine says model I98 250..so im not sure if its the 305/555 engine or not...i'm usually cruising @ 63 or less when i'm loaded..so ur saying faster maybe more efficient for fuel?..What are your thoughts on putting in a chip..Thanks

Spooler

Look on the side of the black plastic valve cover. You will see a Cummins sticker stating the engine type. Hp I think. Smarty Jr. on the lowest settings would be your best option. You may gain about 1-2mpg. What gears do you have.

mmark

Spooler..i really don't know what gears i've got..im sure its just the standard factory gears for that motor..i found the sticker and like i said it showed model I98-250..thats it..sorry i cant get more info..i can call the dealership in the AM and they can tell from the vin what engine type and gears..then i can tell you more...

Spooler

Yeap, get them to pull a build sheet on it. You will know everything.

torquefan

I think the "I98-250" may actually be "ISB 250", meaning you got the 250 horsepower engine available in 2003, and not the 305.

mmark

Turns out my engine is 235hp @ 2700rpm and my gears are 373 of which i have 4 gears..Thanks hopes that helps

Spooler

That helps a lot. You have a 47rh tranny also if you have the 235hp engine. Is that what tranny you have?

A Smarty Jr. will automatically bump you up to the 305/555 engine software, plus some on each setting. Run it on the lower settings and you should be happy.

Lary Ellis (Top)

I agree with the Smarty Jr as well for a couple more MPG...they work well provided you don't use all the added HP that comes with them.

Keep the truck below 70 and Smarty Jr you should do a little better Free Shipping here at the DTR Performance Shop http://www.dodge-diesel.org/smjr03do.html

Spooler

Ordered from TOP before,,,, you will get it quick.

rip 112

Dont know if its in your truck, but in my glove compartment there is a sticker on the bottom of the compartment door that specified the rear end and what gears were installed...just a reference

Spooler

If there is no mention of it he has 3.73 rear gears. Does the build sheet even say limited slip?

sr4440

Might want to check the exhaust, 03's had a ridiculously small 3.5 downpipe to the muffler. FYI i get right @ 14 towing 20K

Joe