i just bought a 98 24v ext cab short bed auto 3.55gears 4x4 i drive about 30miles round trip to work everyday and i cant get above 15mpg this truck is bone stock except a 4in exhaust is this all a stock 24v will do if so i should have bought another 12v or is there possibly something wrong

 

i also have a 1998 24v cummins mine is a 5 speed and i bet i get 18 mpgs.. do you drive with a heavy foot that could be the problem thats my problem sometimes

 

the 3.55 gearing has it's pros and cons....mine has them.

they are good for lowering rpms in case of driving interstate or cruising but for passing and getting up to speed sometimes you gotta give it a little more than you'd want for good fuel mileage. the auto doesnt help either...

first i'd run some good fuel system cleaner through it, change the fuel filter and take a look at the air filter...cheap way to start to see if it helps.

sometimes the egg under the pedal method actually can yield results you wouldnt expect depending how slow you go getting up to speed. taking too long to get to speed seems to actually use more fuel in some vehicles.

another thought is if your wanting to upgrade some stuff, take care of the fuel system and get a small chip or injectors. i see with my edge on level 4 18.5 in town normally and last long highway trip doing 78-80mph with a/c going the whole time, through mountains and traffic, and edge on 5 i got about 23.

 

put an intake cone i suggest BHAF filter, new fuel filter and power services diesel fuel additive, if you wanna spend some money ($200) i suggest a small chip like a diablo sport power puck gives you 1-3 mpg increase

 

Or a set of Bosch RV275s, good for the buck. Gauges first though bud, make sure you keep the VP happy and fueled.

 

alright ill have to look into those and the truck had a new vp and lift pump put on about 15000mi ago so i think it should be good what is a realalistic number that i can expect from this thing sorry just not impressed my old 12v never got any lower then 17 but ill try the air filter and new fuel filter just dont want to dump alot of money into it not sure if i want to keep it yet

 

If you can keep it at or below 2000 rpms about 65-70 mph. You will yield better fuel mileage.

 

I get 22 on the highway with mine. 15-16 in town.

You have stock tires and all? Check the air filter and fuel filter also.

 

BTW I got a Diablo Puck for sale, if you're interested.

Just had a thought, how's your tranny? I'm not too familiar with the autos but I know if they're old and slippin they can really hurt ya.

 

Make sure your fan is free. If the thermo in the fan is stuck it will always be spinning hard which will rob MPGs and power.
Dont run the defrost or A/C.
Synthetic fluids will help.
Run tires at max psi.
Your right foot has a ton to do with things plus the type of driving, as in stuck in traffic, idling a ton and hot rodding.
With my old tires @ 80 psi I could rock 22 mpg.
Towing my boat (4400lbs) just below 80mph with 35"s gets me down to 11mpg.