I have a 2001 1500 sport with the 5.9L engine. Ever since I got the truck the fuel mileage has been kinda weird, one day its great and the next its complete crap. Recently I've been burning almost a quarter tank just going home from work (about 10 miles) and I have pretty much no idea what I'm doing when it comes to finding what's wrong, so any support/help would be great.

 

the first thing i would do is either take it to a reliable mechanic that knows Dodge pickups or get a scanner (wally world has 'em for around $30~40) that reads live data n see what your long term n short term fuel trims are.

 

How many miles on the engine and what does the engine temperature gauge read? On a smooth highway at speed, ease it into neutral and see how it acts. Does it coast okay or slow down right away? Does it steer straight or does it wander and the tires wear oddly?

 

Any codes?

 

Almost a quarter tank is what, 4-5 gallons in 10 miles. The engine would run really crappy or not at all with that much fuel. Assuming the fuel gauge has been verified by filling up, any chance the fuel is escaping via a cracked line or damaged tank or filler hose ?

 

I dont see any leaks or smell any fuel, the guage reads normal when filling up, and I can put about what the guage says it needs into it when I fill up.

 

this is the second engine in the truck and its only got about 70k miles on it, however I wasnt the one to replace it that happened before I got the truck. The temp guage reads right in between 130 and 210. The alignment and everything was just redone not even a month ago so it drives pretty straight.

 

Do a fill up, using the nozzle to sense the cut off, drive your ten miles, then fill the tank again. Have a verifiable baseline to work from.

 

You know, we've been beating this with no result, but now the penny dropped. Head over to Harbor Freight or what ever you have locally, and pick up an infrared remote thermometer. With the engine warmed up to operating temperature. See what the engine is running. With the engine being replaced, it's possible whoever put it in might have put too cool a thermostat in the engine and it's stuck in "open loop" mode. It's injecting extra fuel to warm the engine up but the radiator is cooling it as fast as it warms. If you have a 180 unit, rather than a 195, The old carbureted engines would run a denser charge. Fuel injection though, that doesn't work. Was the engine used or new when it was put in? If it was a used engine, your timing chain might be worn. Check the thermostat first though. It's easier and cheaper than a timing chain.

 

No response to post #4 (ANY CODES) If the motor is not getting up to operating temp it will set a code! And if there are any other issues it will let you know also.