Duramax reduced mileage

[captainmike]

I have the Cummins. My friend has the Duramax, '07 GMC. He was getting about 16 mpg, but recently it has dropped to the 13-14 range. Any ideas?

Any help would be appreciated.

Thanks, Mike

 

[HBarlow]

Perhaps his conscience began bothering him.

 

[Wingate]

hahaha... . thats funny right there, I don't care who you are... jk...

I would have to start with the basics... anything recently done to the truck?. . recent maintenance? new tires? engine modifications?. .

My 03 d-max service truck typically gets 6-7 mpg, but when the injectors start going south, it will drop to a steady 4mpg. I would start by pulling an oil sample to be tested for the presence of fuel and having the injectors tested. Other things that could contribute would be a clogged intake or exhaust system, weak hole, fuel leak (internal or external)... . Could it be that he's changed driving habits?

Personally, i've never seen a d-max get a consistent 16 mpg, but I guess its possible.

 

[Ncostello]

My 2002 Duramax gets a very well documented consistent 18 MPG average with about 70% highway and 30% city driving. If its all highway I can easily document 19-20... although I rarely do all highway driving except on trips.



These are my facts and I have a years worth of data to back it up in a spread sheet including price paid, gallons purchased, miles driven etc etc.

 

[Flying_gage]

If he is farther north, I would say that he starting to experience winter blend fuel. I always lose 1. 5 to 2mpg when it comes online. This fill up my mileage went from mid 17's to 15. 43 this morning.