I have a 96 dodge Dakota 3.9 with around 230k miles. I'm looking for ideas on how to get better mpg. It is doing horribly right now. The truck runs well no hiccups and has a standard tranny. On a full tank I can go about 200 miles. And the exhaust is rich. It has a new distributed and spark plugs. It runs a little cold. The heater core has a good leak also.

 

Sounds like a vacuum leak, but a tune up would be prudent. O2 sensor, clean the mechanicals etc. (ie. TB, intake sensors, and check the vacuum hoses for fouling).

 

Calculate your MPG and tell us, miles per tank doesn't tell us anything.

 

I will hesitantly agree with hahns5.2, not withstanding his internet tone, that there are 2 different fuel tank sizes used, and as such will affect your mileage per tank. I believe one is 14+ gallons and the other is 22 gal. What were you getting prior?

 

15 and 22. And judging by a gas gauge isn't accurate anyways, even if you know how big the tank is. If I tried to figure out the MPG of my B2 by looking at the gas gauge I'd think I was getting 7MPG. Sorry, it's a big pet peeve of mine.

 

+1. There are only two accurate ways to calculate gas milage. The first is to fill the tank up until the gas pump clicks off, drive the truck until empty, and then fill the tank up until the gas pump clicks off.

The problem, however, is that this method only works if your speedometer is accurate. If you have larger tires, or anything else that would throw off the speedometer, this doesn't work. Also, to increase the accuracy, as you are filling up the tank, when it gets near the top, slow down the pump... it will click off at a more consistant spot if its pumping slower.

The second method is to drive the truck until it is 100% out of gas (quits running on a flat, straight road), put a specific amount of gas in the tank, and drive it until it runs out of gas on a flat, straight road.

The problem with this method is that you can get an incorrect result if the truck runs out of gas going around a corner or on a hill cause there can still be gas in it, its just away from the pickup.

 

M milage on my last tank was about 13 mpg. I usually base it on my gas I put in I know better then to rely on my gauge. But there are no oversized tires or extra weight.

 

anybody have a different tank on their truck... mine isn't the 22 or 15 gallon... unless my gas gauge is WAY off. I'm putting about 17 gallons in every time... I think its an 18 gallon

 

1st Generation (1987-96) Dakota's only came with 15 or 22. It is not exact, there is more room than that for fumes and room so it doesn't spill out the seals and vent hoses ect. If you really want to know your size check the tank shape. If is just an rectangle is 15 if it is rectangle with a lip that drops down in the front then it is 22. See pictures below.

The other way to check is check the sticker under the hood. Order a build sheet from Dodge. Some say the Gallon size is stamped in a circle on the tank.

Here are some pics to show.

Here is a 15 Gallon tank.


Here is a 22 Gallon tank.


The green arrow points to the lip that only the 22 has.

 

I would suggest replacing your oxygen sensor. I was having the exact same problem as you; spend $70 to fill my tank (I have the 22 gallon tank) and I do 90% highway and I would get 280-300 miles on a tank (roughly 12-13 mpg). I took my truck into my shop one day and hooked up the scan tool and read the oxygen sensor voltage at .75V, meaning it was running rich. I had did a complete tune up (plugs, wires, cap, rotor, fuel pump, air filter, PCV valve and a brand new double roller timing chain from Summit Racing, 4 Brand new Michelin LTX M/S 2 tires, decarbonize upper cylinder head and fuel injectors,etc.) and I my max mpg was 15 on a trip from Orlando to St. Augustine. After I replaced my O2 sensor, my mpgs have gone up quite a bit (now I get 19).

Also, if you drive 70 MPH, your fuel mileage will drop a little especially if you use A/C. The higher the speed and the faster has to turn, the more fuel you will use. Also, try to stay away from jack-rabbit starts, make sure your air pressures are OK and you should have acceptable fuel mileage.