Hi Guys. I have a 2001 Dodge 3500 dually diesel with the 235hp engine. Truck has 123,000 U.S. miles on it and is stock with no alterations or chip etc. Up until recently my fuel economy has been good at about 23 mpg highway or better. I live in Canada, ( Imperial gallon up here ) I am now getting about 14 to 16 mpg. I checked over several fills. My driving is mostly highway, about 90%. I changed my air filter around the time this problem started. New from the Cummins dealer. Is it possible that a faulty air filter could cause a drop in mileage like this? Truck seems to lack some horse power too but runs smooth otherwise. Any suggestions?

 

Have you checked your fuel filter lately, if its plugged it will cut back power and that will cut back mileage. if it is a stock air box make sure it hasnt sucked or colapsed the filter and is blocking the itake, good luck

 

Was the mileage change over time or more like overnight? Figuratively speaking.

 

Bingo. Fuel filter was filthy. Must have picked up some bad diesel somewhere. This problem seemed to show up in a short time. It has only been about 15,000 miles since I changed it. Now engine feels like it has more snap to it. I will start another mileage test. Hey Thanks Guys!
01 Dodge 3500 235 hp stock

 

How fast are you driving? That isn't very good mileage if you are going 55, but it is wonderful if you are driving 90. Speed counts for a lot more fuel use than weight.

 

best to carry a spare fuel filter under the seat, all the time. it only takes 1 tank of bad fuel to plug up a filter....
if you had a fuel pressure gauge installed, you would know immediately that there was a fuel suppy issue,
welcome to the forum, do searches for lift pumps/fuel pressure gauges, a little reading will save you the cost of a VP

 

I am getting 13.8 average is this low?

 

To me it is, is your truck lifted, or a stock automatic with virtually all city driving?

 

I just drove from Grand Jct Co. to Williston North Dak. Ran 85mph most of the way. Get the best mileage with the flashpaq set on perf. I got 16mpg all the way. Seems low to me. Fuel psi is good. Stayed at 18/19psi. Tranny just got rebuilt. This was its maiden voyage. New tq conv, overdrive housing and piston, sure shift kit, pump rebuild, 2nd gear band, rev band, filter, fluid. And some other stuff I can't recall at the moment. Also changed the oil the day prior to leaving. I think this is pretty poor mileage, but my buddy with a powerchoke says that's pretty good for running 85. What do you guys think?

 

Nope stock automatic no lift.

 

Sorry, the day I can get 16 MPG out of a full size truck running 85 MPH is the day I celebrate.......

That is pushing one whale of a brick.

 

Boy, I'm with ya on that one. Seems a little nuts to me to be driving like that anyway. What's your big hurry??? Afraid you'll miss your own funeral?

Sorry, I couldn't help it. I spent 27 years pulling people out of wrecked vehicles so I have a bit of a gallows humor sometimes.

 

Yep, 85 seems awful fast if you're at all concerned about mileage. I try and keep it under 70 normally. Any faster than that and mileage starts to fall off a cliff.

And then there is basic safety, as Russ points out.

 

Russ Roth I agree I tell everyone I pull over that until they get to go give a death notification they will never understand why Law Enforcement comes down on speeders and crap. I have had the privilege to do quite a few and would be happy if I never had to do it again.

 

Thats exactly what mine gets and the ironic thing is they look like the same truck lol... except mine is a short bed...

Previous owner said he averaged 18 city and 22 highway empty and 16 pulling his car hauler... i bought the truck not running and one of the first things i did to get it going was new vp and airdog 100... The overhead still reads this but i avg 13.8 -14.2 mixed driving not over 72 on the highway stock hight and 265 tires.. I think this is normal for the stock auto tranny... Thank goodness the new goerend unit should be here in a week or so