Alan Pritchard

Help, I have a 2003 Doge 2500 Quad Cab Short Bed, SLT with a 5.9L I-6cyl Cummins,
I got the Cummins because everyone said how great the mileage is when they are towing, The truck has 373 gears and has 275/60 R20 Tires, The previous owner had removed the catalytic converter, Added a K&N filter and a Diablo sport. When empty and on the interstate 2000 RPM 73MPH I get 18.5MPG and at 1500 RPM 53MPH I get 23MPG.
I have a 28ft TT and it is 7000lbs loaded at 2000 RPM, The truck gets 9.5. I do live in KY so we do have hills but I got this good with my Hemi.

John Faughn

The tire size is got me wandering if you have issues there to start , do you really have 20 " tires ?
Next is wider get less millage , not sure what the width is stock , but may have been 16-17" rims .
So with starting there I would also be suspect of your numbers , how do you know that they are correct , taller tires & odometer , has there been correction ?
Next is 3:73s , I thought that dodge should have stayed with 3:54 , 4:10s as the choices , better millage with the 3:54s , modding to get the power & TQ good .
From what I have seen , towing has lowered millage by about 25% , like on mine , about 19-20 unloaded , 15 pulling Airstream [ about 6,000 lbs ] .

Alan Pritchard

I guess I will take it back to the dealer and have them run a diagnostic check and see if something is wrong with it, I will also see if they can adjust the tire size. It only throws to speed and the overhead computer off a little. I go by mile markers and GPS mostly. If I keep it I am thinking of using Amsoil synthetic oil and maybe the Banks Ram Air. What do you think about Amsoil?

John Faughn

What size tires do you have ?
I have not heard of 20 " tires .
I suspect that it is out of warranty , and that taking to dealer has a long rep. of problems .
How long have your had it ?

.boB

There is a good selection of 20" LT tires available. Be sure and check the load range, though. But, those 20" wheels are part of the problem. They're pretty heavy, and take a lot of power to move them around. Takes a lot of braking power to get them stopped, too.

Get rid of the K&N filter. When new, it flows better than stock. But, very quickly it flows significantly less than stock. Best long term performance comes from a quality paper stock-type filter.

There is no evidence at all that an aftermarket air cleaner set up does anything for a stock or lightly modded truck. A complete waste of time and money.

Synthetic oils like Amsoil will help mileage a little bit. But not enough to balance out the expense. You'll get the same benifit using a "fake" synthetic like Mobile 1, Valvoline, QS, etc, for about 1/2 the price.

Totallyrad

A couple other things. If you're going by the overhead computer, don't. It's usually way off. Next, you've got to get below 2000 rpm. With the 3:73 and stock tires 2050 rpm is 70 mph on my truck. You've already seen a significant mileage increase lowering your speed and the same applies while towing. I use a TAG, Air Raid Jr. and a Smarty with the low smoke program they ran on the Jr. and can get 20 empty and about 11-12 towing 12k.

03 ant a hemi

When empty and on the interstate 2000 RPM 73MPH I get 18.5MPG and at 1500 RPM 53MPH I get 23MPG.
I have a 28ft TT and it is 7000lbs loaded at 2000 RPM, The truck gets 9.5.

Running 2000RPMs with your trailer in tow will net you bad results in milage. DOn't care what you do with your truck. What mods you do with it you will get bad milage. When towing keep it in the 1500-1800 range and that should net you better milage.

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rip 112

I have 20's too, and pulling my TT (5-6k lbs) I can manage 13-15mpg from 65-70mph average. Unloaded I get about 19 hand calculated, 20+ if its a long trip...

Make sure all you filters are clean, and make sure you're on a towing program or back to stock. Do you have gauges???

Alan Pritchard

I have tried to go back and forth on the tunes to see if it makes a difference, Today I cleaned the air filter put it back on a tow tune and got 10MPG at 2000 RPM 70MPH

This past weekend five of us went to the smoky mountains. Two of us have Dodge and 2 have Fords one has GMC; they all got better than I did. The Dodge dully got 16, Fords around 13 and the GMC 14, we all filled up at the same time so we could compare MPG. I felt ashamed to only get 10.

I dont have anything but stock gages,No boost or temp.

But hey my truck is paid for also.

moorepower

I would suspect the 20" tires are a major downer on the mpg. When my truck was new it got 12-13 mpg towing a 26' TT, but I kept it under 65. Wind resistance and rpm kill the mpg's. I swear by my smarty beta 4.4 on level 3 for mileage and power with an 03. It is by far the best thing I have done for fuel mileage.

Alan Pritchard

Hey every one I got it fixed. I took the truck back to the dealer and told them to flash the computer and give me any updates, after about an hour or so they finished it and I was on my way. I am keeping it! I averaged 23mpg on the interstate and 19 to 20 combined. I will give it a towing test next weekend; I will be going to Lake Cumberland.

CRToney

Check out the mods in my sig. Most add power and some milage.