I thought i'd be getting better mpg. The truck is 1998 12v 4x4 dually stock auto trans with 3.55s...mpg on hwy 17 traveling at 70 mph and city 14.5.

Ive done all filters, is this what they normally get?

My friends 2001 dually gets 22 hwy and 19/20 city non 4x4.

 

i have a 97 12v 5spd single cab long bed and get about 22 to 24 highway and in town about 20 to 21. my buddy has a 96 12v single cab long bed with a suncoast auto and a 01 24v ext cab long bed and a ats auto and he does good to get 14 in town and 19 on the highway. but the 96 does do a lil better then the 01. my personal opinion is that the automatic does not do near as well on fuel mileage but that is mine.

 

ive got 27 highway and 23 city till i started having problems

 

26 Highway (avg 70mph) and 19 City (Heavy Right Foot)

I made a 150 mile trip empty at 65mph, drove around town maybe 50 miles, then pulled an 18' bumper pull with a Jeep on it back 150miles. Averaged 21mpg on that trip. Mines 2wd and 5-spd with 3.55's though.

 

How can i get better mpg ? Is auto trans that bad?

 

Auto tranny's on the older dodge diesels havn't been the best.They can handle stock power o.k.But start dumpin alot of power to them and they start acting up.Mine acts up sometimes.I get 17/19 city and 22/24 freeway.Is your truck stock?A few good ways to help increase your milage is to help the engine breath better.1)The stock exhaust system can be very restrictive,You want to help the exhaust gasses leave the engine easier.2)You can also add a better air filter,that helps the engine breath easier.Hope this helps.

 

last tank i got 20.88mpg
you might try some injecter cleaner and your timing could of sliped also.

also i'm runing 15.5* of timming

 

Set your timing at around 16*, put on a 4" turbo back exhaust, get a good intake system on there. That stuff should help. What type and size tires are you running? 265s in a mild highway tread will do alot better than 305s in a mud terrain.

 

You won't see the same mileage as a smaller/lighter truck or a truck with a manual transmission. I've been surprised that my truck gets the mileage it does for being such a heavy truck. I weighed in at an empty 6600lbs at the scrapyard.

The 4x4 adds weight, as does a larger truck cab or dually rear axle, which puts more load on the motor. Large tires will also hurt fuel mileage since they are unsprung weight and more rotational mass. The Automatic transmission uses more power to spin the tires, so you have to compensate for a larger loss of drivetrain power with the slushbox automatic over a simpler manual transmission.

Your best bet is to do proper tuning (ie: pump timing, fuel plate, air filter, exhaust, etc.) Transmission upgrades should not only make your automatic stonger and more capable of holding up to higher torque, but also improve mileage by having less slip and tighter shift points.

This goes for all vehicles, but diesels have an advantage over gasoline because we can make major power increases without sacrificing reliability or fuel mileage. My old 1st Gen was a reg cab 5spd 2wd with 3.55's and 285/75/16's out back. When I first got it, I was averaging 20mpg on the highway. After modifying it up to 341hp/842lbft at the rear wheels, I was getting 24mpg on the highway. Making the motor have more power means it doesn't have to work as hard to drag the weight around.