Fuel mileage tracker all over

[14SierraZ71]

Just a quick question if anyone else has noticed this or had this problem. On my way home on the same highway I always take with the same fuel, load etc.. I noticed on the DIC that my mpg tracker was fluctuating a pretty decent amount. Normally it bounces between 1-2 MPGs at steady highway speed but tonight it had a 5-7 MPG fluctuation. I have a blackbear tune with v4 delete, Cai, oil catch can and Borla cat back exhaust. I didn't notice any surging or pulsation of the rpms gauge and there wasn't any wind at all pushing me around. Kind of confused what's going on here..

 

2014 GMC Sierra 5.3L 4wd

[BigBadSierra]

Any kind of wind can cause this even if you can feel it or not. My truck never gives the same millage week to week it's slightly different. Drive the exact same way every day.

 

These trucks are big and the air around them seems to come into play even just from being behind another vehicle.

[14SierraZ71]

So yea on the way to work this morning on the same highway under all the same conditions it showed a steady fuel consumption. You got me

[Sierra Dan]

Wind is a huge factor.

Mine can fluctuate as much as 3-4mpg average with the slightest headwind and it stays in V8 mode longer.

It's funny to watch how far it drops fast idling as well.

[swathdiver]

Yep, drives me nuts when trying to do mileage calculations, even at night when there's less wind.  Get behind a rig and watch the instant economy shoot up, pull around him and into the wind and watch it drop by half!

[Sierra Dan]

12 minutes ago, swathdiver said:

Yep, drives me nuts when trying to do mileage calculations, even at night when there's less wind.  Get behind a rig and watch the instant economy shoot up, pull around him and into the wind and watch it drop by half!

Amen!

[Darmichar]

3 hours ago, BigBadSierra said:

Any kind of wind can cause this even if you can feel it or not. My truck never gives the same millage week to week it's slightly different. Drive the exact same way every day.

 

These trucks are big and the air around them seems to come into play even just from being behind another vehicle.

This.  Have now owned the 2014 LT and 2018 Z71 and see radically different MPG's with just a few MPH of wind.  I live in Central Illinois where winds can get up to and sustain 30+ MPH easily.  A good headwind like that at 65 MPH and you're lucky to pull 16-18 MPG when I would normally see 22-23 on a calm day.

[Sierra Dan]

1 hour ago, Darmichar said:

This.  Have now owned the 2014 LT and 2018 Z71 and see radically different MPG's with just a few MPH of wind.  I live in Central Illinois where winds can get up to and sustain 30+ MPH easily.  A good headwind like that at 65 MPH and you're lucky to pull 16-18 MPG when I would normally see 22-23 on a calm day.

Surely your numbers are Average for city and highway?

I have never averaged 22-23 on mine. That would be a miracle.   

[Darmichar]

35 minutes ago, Sierra Dan said:

Surely your numbers are Average for city and highway?

I have never averaged 22-23 on mine. That would be a miracle.   

I tracked every drop of fuel that went into my 2014.  In perfect conditions (warm/calm/flat, etc) my truck with a Leer topper would easily average 22-23 MPG on long highway trips.  Hook the boat to it on a windy day and I was lucky to get 9MPG out of it.  When I traded it in I had averaged 15.11 MPG over the life of the truck.  22-23 MPG didn't hapen often, but it is attainable in these trucks.  That was with a 3.08 rear.

 

I just drove my new truck to Pittsburgh, PA over the weekend and on the first leg of the trip out there I averaged 22.21 MPG on the first tank.  20.22 MPG on the trip, overall.  That's with a 3.42 rear.

[Sierra Dan]

3.08 rear.

 

No wonder LOL

I have a 3.42

[Darmichar]

1 minute ago, Sierra Dan said:

3.08 rear.

 

No wonder LOL

I have a 3.42

Also, the MPG reading in the DIC is lies, it is *easily* always over by 1 to 1.5 MPG in its estimates when compared to real, calculated MPG.

[Sierra Dan]

I have read also where manual calculation is more accurate. But 1mpg for the computer to estimate for me saves a lot of time LOL

[Dr Awesome]

My DIC is off by about 2 mpg high every time I calculate, it's kind of annoying, I would have expected more accuracy.   It's not like I bought it for the mileage, but for the people who never calculate it manually, it probably looks pretty great!

[swathdiver]

My DIC is within tenths of a mpg compared with hand calculations.  Tonight for a spell the best the truck could muster was 14.5 mpg @ 70 and then to 16, probably into the winds.  On the way back it went up to 18.6 mpg @ 70 mph on the same 50+ miles of road just a little cooler and the sea breeze gone or tamped down.  Don't fret, mine is GMT900 not K2!  

[tnchevy]

I have tracked my mpg's since I bought the truck (hand calculated and put on a spreadsheet).  My truck's lifetime mpg's has been slowly decreasing in the 4 years I have owned it.  The first couple of years it was 19.5 mpg avg but now down to a lifetime of 19.1 mpg's.  I only drive 5-6k miles a year so I am just at 25k for the 4 years but still disappointing since every other vehicle I have ever owned got better mpg's after the engine was broke in.