I got a brand new D/A LLY in Feb. My firtst few tanks, I was getting 18+ MPG. Now, a little over 4000 miles later, I'm only getting about 13-15 MPG by manual calculation.


I took it into the dealer to whine about the situation. They plugged the computer into it and said there were no error codes. They said nothing was wrong, "but you should keep an eye on it".


Well, my driving locations or habits haven't changed. I've been using fuel from differtent suppliers. My mileage is going downhill, when it should be getting better.


The computer says everthing is fine, but logic tells me that my mileage should not be going down. Something is wrong somewhere.


It seems to me like the Tech's. rely totally on their diagnostic computer(which I can understand to a point), but how dependable or how much can you trust the computers?? I don't know!


Any suggestions or advise would be greatly apprecited!!!!!


Thanks,


Ron

I have found my mileage fluctuates also. I think it is the fuel supplier. If I get bad mileage I try another station.


Scott

rgelfan,

Check your oil and if your mileage really drops fast look for overfilling of the crankacase. Better safe than sorry.

Your mileage is supposed to drop once you get the vehicle out of the showroom. All of us Duramax owners know this, as do all of the GM dealers. We all talk about increasing performance and mileage as you get more miles on the engine, but none of it is true. Your MPG should continue to decline until it settles in at about 9.5 mpg at 50,000 miles, at which point the injectors will fail.

I have experienced a bad tank or 2 where mileage was below 15. But refilling at the normal stations and she fine again.


I do notice that i lose 1 mpg on avg during the summer, probably due to Air conditioner