I experienced a pretty close to a drop of 4 MPG in a couple days with the same driving patterns. I used to get around 20 and now my roof console is reading around 16. I also have noticed my truck is running a bit warmer than usual too (I know its not due to the heat either). I was wondering if a sticking thermostat would be the cause of these by any chance? The rad fluid was changed in march but not to sure if it was flushed. Any comments would be great thanks.
My truck is a 2004 3500 5.9L

 

Im not much of a 3rd gen guy but from what Ive heard those consoles lie big time.

 

Do get your fuel from the same place always? I have seen over 5 mpg difference on paper from where it came from. some fuel is just junk.

 

well i hope so...i haven't experienced this before, i just got the truck acouple months ago and i was avgin 18ish in town and 20 on the hwy....i replaced my air filter and got it up to almost 23 on the hwy...now its down to 16 city and 18ish hwy...but it just changed over one tank...maybe bad fuel? I fill up at the same place always, maybe its time for a new fuel filter, not sure when that was changed...but one tank it shouldn't change 4-6 mpg!

 

i always get it from the flying j...its a truck stop here in kamloops...its a shell station with about 14 pumps

 

I have more than once gone on a trip to a place, no fill up. come back part way home, filled up, and had to fill it up one more time to get home. And yes it still 3/4 full when I got home but. 20+ mpg there, 14 or so on the next load of junk.

 

ya i hope its just the fuel....i have the maintenance records for the past couple years for the truck and where it was dealt with. They said it was always looked after well and when ever anything need to be done it was....im hoping bad fuel is the culprit...i'll find out next fill i guess...thanks

 

Fuel additive is always used on every fill as well

 

If you are only going by the overhead lie-o-meter you could be chasing your tail. You need to do hand calculations to know for sure.

I rarely look at the overhead for MPG now but for a while I did. It would show 22 very regularly even though I was only getting about 20 hand calculated. It dropped one day to 15 and I got concerned. Drove that way for two days and filled up and checked and was still in the 20 mpg range. I hit "Reset" and drove for a while and it went back to 22. So long story short...... hand calculations are the ONLY way to know if things are changing.

 

well all the info is much appreciated...im new to theses teck gizmos so i'll just keep an i on things

 

The overhead is just a reference, and a poor one at that!

 

I figured out my temp problem.. my clutch fan wire is shredded thats going to be about $250 :S

 

any know of a pdf file that shows the replacement of this?

 

The overhead readout is a good reference if one knows the correction factor. I use mine all the time to "read" winds, etc.