We've often theorized here about what the overhead does to calculate average MPG. After an experience this weekend I'm confident it's not "since the last time you pressed reset".

Over the weekend I was near the end of this last tank, meaning I had ~500 miles since the last MPG reset. I made a highway trip to our lake house, going ~70-75 on the way there (interstate) and ~55-60 on the way back (state highway). We all know there's a real knee in the curve above 60 MPH in these trucks, and WOW could you see it on the outbound trip. My overhead was dropping in near-real-time, losing tenths every couple of miles. I went from 19.0 to 18.3 in about 20 miles of 70-75 MPH driving. On the inbound trip at 55-60 it gained a tenth every couple until I was back up to 18.8.

My point here is that, with ~500 miles since the last overhead reset, a round trip of ~60 miles could not have had that much impact on the MPG. Therefore I believe the overhead has some narrower window that looks back only "so far", not necessarily as far as the last reset. We may be fooling ourselves believing that the overhead reflects the MPG for the entire tank - it may be more of an intermediate calculation between the "full tank" value and the "instantaneous economy" reading that was on older trucks and is still available on other DC vehicles such as minivans and some Benz sedans.

Based on this behavior, I now use it as a relative indication of how my efficiency is doing "over the last little while".

 

Hey how are you gettin that good of gas milage i am short shifting like a mother to get better fuel econmy but do you jus drive on the freeway..because i cant get my in town above 16 by my calculations...

 

Nope, as stated this is mixed city/highway driving. I drive to work ~20 miles round trip each day, plus the occasional evening/weekend stuff. I'd estimate 60% city at 40 MPH and below, and 40% highway averaging 60 MPH.

I'm driving "normally". Mostly respectable starts and stops with the occasional "quick off the line". Most upshifts are done around 2K RPM. I do have a weakness for uphill climbs, though, and there are a few quiet, empty roads around here that the truck seems to like use for exercise (i.e. accelerating as fast as possible from the bottom to the top [grin]). Those usually involve upshifts closer to 3K RPM. Hearing that turbo spin up while you're gaining speed AND altitude is really inspiring. I'm sure that impacts my MPG but it's good for the engine to work harder once in a while.

Anyway, I don't have an explanation for your low mileage. Like I've said, if anyone is getting low mileage they should complain at to the Dodge service folks and make them fix it. Have you confirmed the rev level of your firmware? Perhaps a TSB reflash would help.

 

Well i work up in the hills and stuff around lake tahoe.. Could the elevation be part of it.. I did make it back here from southern california on one tank and that was about 700 miles but.. I might try the reflash.. i have had it done once and it helped out a lot.. I already have 13000 miles on my truck.. So it is broke in from what i beleive.. Well i will have to see what happens if i get it reflashed

 

I doubt elevation affects it much. The turbocharger should keep your air nice and pressurized.

 

Yeah well i will blame it on all this hills and my liking of hearing that turbo spool up...I have a heavy foot sum times but i usually drive like a grandma..

 

Mine seems to read ~2.5mpg hi. Empty, OH read 17.8....Hand calc at 15.3. MPG overall seems OK for just 1200miles. W/ 4500lb boat, OH read 14.6...Hand calc 12.5.

Tony

 

Wactd and Ripper,
What the heck is wrong with this picture?? W...Are you reading the overhead or hand calculating? And Ripper.....First off, have you figured in the big tires, and secondly, I don't see in your sig that you have installed an auxillary tank. Your sig does state that you have a shortbed, which has a 34 gal. tank. If you really pulled 700 miles on a a tank,you are pulling all kinds of mileage! What am I missing here?

 

Mine reads anywhere from 1.5 to 2 mph high when I hand calc as well. I've tried both reseting it at a stop with the key in the AUX postion as well as rolling down the road. No differance what so ever.

My 04 was aways with .2 or so.

 

As stated in the text and my signature, my MPG is hand-calculated and I carefully top off the tank every time so I know for certain it's the same amount every single fillup.

These are real numbers. And I'm very happy about them!

 

I hand calculate my **** i dont use the overhead.. But i dont get how i got such great mileage on that trip and get such poor fuel mileage now...