17 MPG city driving (not 22) on 2021 Sierra 1500 AT4 diesel (3.0)

[Grumpy Bear]

8 hours ago, domerdel said:

Hi everyone,

 

I've put about 1400 miles on my new 2021 GMC Sierra 1500 Duramax Diesel

What other factors should I consider to improve MPG?

 

This will improve as miles are accumulate.

 

Personally I've never owned a diesel but my gas motors peak somewhere after 50,000 miles (80,000 kilometers) Air cooled a bit quicker that water buffalos.  Be patient. 

[KARNUT]

My wife’s and my mileage usually varies by 5 MPG. I’m kinda of a lead foot sometimes she’s less so. I get the better mileage. The difference. I anticipate stoplights. She sits in the car with it running after swimming eating a snack or lunch. I got curious once and asked if she was street racing.


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[Descartian]

17 hours ago, Grover67 said:

If you have winter blend fuel out there it will reduce your mpg also.

-Grover67

Winter diesel will give you significantly lower MPG. 

[mjonesjr84]

14 minutes ago, Descartian said:

Winter diesel will give you significantly lower MPG. 

It will give you lower, but not significantly lower. You can expect 1-3 mpg lower. What gives you lower mpg is a lot of idling to warm the truck up.

 

If I get significantly higher fuel mileage when summer blend hits, I'll be well north of 30mpg in a 4x4 crew cab truck.

Edited March 5, 2021 by mjonesjr84

[newdude]

49 minutes ago, mjonesjr84 said:

It will give you lower, but not significantly lower. You can expect 1-3 mpg lower. What gives you lower mpg is a lot of idling to warm the truck up.

 

 

Bingo.  This was consistent in my 2016 Colorado Diesel when I had that.  I would regularly average 26-28mpg per tank spring/summer/fall and 22-24mpg come winter from all that 10+minutes of elevated idle warming up.  22mpg was my worst and that was during a cold snap we had for a couple days.  

Edited March 5, 2021 by newdude

[Grumpy Bear]

Winter summer swing is more about lubricant temperatures than fuel composition. Four plus years of my gas motor mileage. Can you pick out the summers versus the winters? I don't warm up anything. Start and as soon as oil pressure is stable I'm moving. The smaller swings within a season are windspeed  and trip speed/length influenced. 

 

[redwngr]

In winter it also takes longer for the transmission to warm, the differential(s) and the transfer case.

 

Once the truck is warmed up, If you drive the epa city loop you will likely get the epa city loop mileage.  

 

The odds of anybody's usage being the same as either epa loop are extremely low.

But it does give a way that expected mileage of 2 vehicles can be compared.

 

 

Leave the '25 mile average' screen up for awhile and watch what it does under different driving conditions. 

Usage (and temps and wind) makes a huge difference.  Driving the same stretch of road at different speeds and in different weather conditions will give different results. (yes, I realize that sometimes there is little choice about speed and stops/starts --- but I often I'm running where there is little traffic)

And it shows that while mileage comparisons between owners might be a little entertaining, it is mostly a waste of time. 

 

 

 

 

[Grumpy Bear]

2 hours ago, redwngr said:

In winter it also takes longer for the transmission to warm, the differential(s) and the transfer case.

 

 

Oh boy yes and wheel bearings never reach summer temperatures. I do coast down test often. The difference in a fully warmed truck at 85 F and one fully warmed at 0 F is over 100 yards from just 45 mph to 30 mph. 

[mjonesjr84]

Something else to take into consideration is have you made sure your tires are inflated to the recommended PSI? Cold weather will lower the PSI in the tires.

[joostan]

I flipped my tow mirrors in today to see if that makes a difference on mpg. Going 60mph, Maybe 0.5mpg

[Wormydog1724]

18 hours ago, joostan said:

I flipped my tow mirrors in today to see if that makes a difference on mpg. Going 60mph, Maybe 0.5mpg

I’ll try that on my next trip to the mountains across desolate northeastern New Mexico 

[TweetybyrdRT]

I spent the last week commuting in and out of LA from Oxnard, about 55 miles each way in mixed freeway and town driving (101 freeway and sunset Blvd) taking into account normal LA traffic and one day La traffic in the rain.  I averaged 24.9 MPG  in My Z71 RST

[Xterrable]

My AT4 came with the Goodyear "street" tires.  One size smaller then the Duratracs.  I think they were 265/65/18.  I was getting a pretty consistent 22 MPG up to 31.5 MPG at 55 mph for over an hour.  I swapped out my setup for TrailBoss wheels with the Duratracs (factory size 275/65)) and saw an immediate drop of about 1.5 MPG.  I then went 1 size up to a 285/65/18 and saw about another 1.5 MPG drop.   A lot has to do with weight and rolling resistance.  

[Wormydog1724]

On 3/7/2021 at 9:26 AM, Wormydog1724 said:

I’ll try that on my next trip to the mountains across desolate northeastern New Mexico 

 

 

So I did fold my mirrors in for a good 100 miles across northeastern NM and I'll be damned, I think it did make a 1 to 1.5 mpg difference. 

 

I had a generous tailwind and was getting 29-30mpg on the 50 mile average! The entire trip 250 mile trip averaged 25 mpg which is the best so far. On the 25 mile average coming through the canyon I got 48.9mpg, I'll be trying for 50mpg next time lol

[gemarsh]

Just got thru with a cross country vacation. First screen shot is going thru part of Missouri and Nebraska, heading home. Looks like speeding helps fuel mileage!

 

Second screenshot is mileage for this month. Lots of mountain driving in Virginia mountain tops. Tennessee wasn't near as bad.

 

I don't drive it to try and get fuel efficiency, I drive it to get the torque feel.

 

Can hardly wait for summer fuel.