Fuel efficiency drop in newer models ?

[WalleyeMikeIII]

I get about 32 with the cruise at 60 or so, on level ground. 2022 5.3 Tahoe, 4x4.

I am not sure I believe that...you have the distance set at 25 miles, so computer calculating your BEST 25 mile score and your AVG over the last 25 miles driven.
Flip the page to the screen on the current drive or for Trip A, and see what the computer calculates the MPG for over 200-300 miles...
I'd be seriously impressed if your Tahoe averaged 32MPG over a 200 Mile drive...

 

[Big Mama]

The only way Big Mama could get 28 mpg is if I was going downhill with. 60 mph tailwind and the GM optional sail package was activated. Your 2018 is incredible.

 

[vcode]

I am not sure I believe that...you have the distance set at 25 miles, so computer calculating your BEST 25 mile score and your AVG over the last 25 miles driven.
Flip the page to the screen on the current drive or for Trip A, and see what the computer calculates the MPG for over 200-300 miles...
I'd be seriously impressed if your Tahoe averaged 32MPG over a 200 Mile drive...

Agreed. No way will you get better mileage than a diesel. No way. If that is real, GM would buy that truck for a million bucks to see what magic is going on there.

 

[PPK_]

Hi all,

We just bought a 2024 Suburban Z71 with the 5.3 and 10 speed transmission... now before I go further, I am not very concerned about fuel efficiency (otherwise we wouldn't have bought the vehicle) I am simply making observations and expressing some level of disappointment in engineering decisions that haven't benefited everyone...

Compared to the 2018 with the 5.3 and 6 speed transmission we used to have we are noting that real world fuel efficiency

- in the city is slightly better in the newer model (13mpg vs 15mpg)
- on the highway we are noticing a significant drop in fuel efficiency. On our 2018 if we drove it well we averaged 26-27 mpg whereas on the 2024, we are maxing out at about 18 mpg... (when we had the Range AFM dongle plugged in on the 2018 we still averaged about 24-25mpg...)

The low-end torque was also honestly better with the 2018 with the 6-speed transmission.

The official ratings (from fueleconomy.gov) are definitely supportive of our observations that the outgoing models were better in fuel efficiency.

No change in Tow ratings vs the outgoing model

I loved the 6-speed and it was easy to service and maintain (relatively easily dropping pan, change filter, change fluid, monitor via dipstick). The 10-speed's oil pan is right under the exhaust and looks like both the driver and passenger side manifolds have to be undone to even drop the pan.

I don't see any articles or discussion over this. Being in the engineer profession myself, I am not seeing a better "Figure of merit" with the new technology. Hopefully somebody can educate me on what I am missing.

i think mpg is worse.. if you are comparing E10 to E10 after '22... e10 is now actually E15.. current administration helped out the farmers upping the mix to 15%.... even though the tank says is it is 10%...

 

[WalleyeMikeIII]

i think mpg is worse.. if you are comparing E10 to E10 after '22... e10 is now actually E15.. current administration helped out the farmers upping the mix to 15%.... even though the tank says is it is 10%...

Depends on the state. In MN, e15 is marketed as “Unleaded 88” since the extra 5% boosts the octane a bit.

 

[Fless]

Many States require such labeling, but some do not. Patrick De Haan from GasBuddy tells us which ones don't:

Does your state require ethanol labeling? - GasBuddy

It's a fact that many know about ethanol- it contains less energy than conventional gasoline, and results in lower fuel efficiency. Some states have moved

www.gasbuddy.com

Spoiler: California, District of Columbia, Hawaii, Indiana, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Missouri, New Jersey, New Mexico, North Carolina, and Ohio

 

[viven44]

I'm starting to think this whole 10 speed thing is not making any sense.... my thoughts are along the lines of having too many gears without the return on investment. Feel free to poke holes in my line of thinking.

Looking at the final drive ratio

4L60-E - 0.70, 3rd gear is 1.0
6L80 - 0.67, 5th gear is 0.85
10L80 - 0.64, 9th gear is 0.69, 8th gear is 0.85

I noticed the engine RPMs being really low on my 2002 Yukon when it goes into 4th (Final gear) at about 50 or so and the engine really lugging through it.. rather well because it is a pure V8 running like a V8.

The problem with the newer small blocks on the 10-speed is that they are unable to lug through the final gear until true top speed, or if/when they can they cannot deactivate cylinders... so the final drive gear doesn't kick in really late... it is probably running higher time-speed-averaged RPMs overall vs the 4L60 and the 6L80.

Cylinder deactivation with more gears should in theory result in more optimization for fuel economy, but evidently they are doing a better job on the 6L80.

So i'm starting to understand GM's handicap. They just need to get rid of the extras and focus on what is best for longevity and fuel economy

 

[ivin74]

I get about 32 with the cruise at 60 or so, on level ground. 2022 5.3 Tahoe, 4x4.

Is this with the duramax engine?

 

[Marky Dissod]

I'm starting to think this whole 10 speed thing is not making any sense ...
my thoughts are along the lines of having too many gears without the return on investment.
Feel free to poke holes in my line of thinking.

Looking at the final drive ratio
4L60E - 0.696, 3rd gear is 1.0
6L80 - 0.667, 5th gear is 0.852
10L80 - 0.636, 9th gear is 0.689, 8th gear is 0.854

Not poking holes, more like filling in holes ...
10L80: ... 4.69 ... 2.99 ... 2.15 ... 1.77 ... 1.52 ... 1.28 ... 1.000 ... 0.85 ... 0.69 ... 0.64 (7.32 Spread)
8L90E: ... 4.56 ... 2.97 .... 2.08 .... 1.69 . . . . . . . 1.27 ... 1.000 ... 0.85 . . . . . . . 0.65 (7.01 Spread)
6L90E: . . . . 4.03 . . . . 2.36 . . . . . . . . . 1.53 . . . . 1.15 . . . . . . . 0.85 . . . . . 0.67 (6.01 Spread)
4L60E: . . . . . . . 3.06 . . . . . . . . . . 1.63 . . . . . . . . . . . . 1.000 . . . . . . . 0.70 (4.43 Spread)

OK, now multiply by a 'reasonable' axle ratio (the often forgotten step!)
10L80 x 3.23: ... 15.15 ... 9.66 ... 6.95 ... 5.72 ... 4.91 ... 4.13 ... 3.231 ... 2.75 ... 2.23 ... 2.07 (7.32 Spread)
8L90E x 3.23: ... 14.73 ... 9.60 .... 6.72 .... 5.46 . . . . . . . 4.10 ... 3.231 ... 2.75 . . . . . . . 2.10 (7.01 Spread)
6L90E x 3.23: . . . . 13.02 . . . . 7.62 . . . . . . . . . 4.94 . . . . 3.71 . . . . . . . 2.75 . . . . . 2.16 (6.01 Spread)
4L60E x 3.23: . . . . . . . 9.88 . . . . . . . . . . 5.27 . . . . . . . . . . . . . 3.231 . . . . . . . 2.25 (4.43 Spread)

If I knew how to better spread those numbers out for a more visually accurate representation, I would ...
Many more underdriven gears that have also gotten more assertive have noticeably improved city MpG (and acceleration).
BUT
Despite more underdriven gears, the final gear ('times') the axle gear, ain't never gonna be under 2 in a truck / suv.
Hence lean cruise, followed by Engine Half@$$, followed by Cylinder Confusion, and highway MpG has improved,
just not by as as much as city MpG.

Note:
3.23 is a decent axle gear for 10L80 or 8L90 (does GM even bother to offer an axle gear besides 3.23 anymore?).
3.23 is passably inoffensive for a 6L80 (GM offered 3.42, 3.73, and rarely 4.10 for heavier and heavier-duty 6L90 vehicles).
3.23 sucks chapped unwiped @$$ for a 4L60E, explaining why GM offered 3.42, 3.73, and 4.10 far more often for heavier 4L60 & 4L80 vehicles.

 

[viven44]

Not poking holes, more like filling in holes ...
10L80: ... 4.69 ... 2.99 ... 2.15 ... 1.77 ... 1.52 ... 1.28 ... 1.000 ... 0.85 ... 0.69 ... 0.64 (7.32 Spread)
8L90E: ... 4.56 ... 2.97 .... 2.08 .... 1.69 . . . . . . . 1.27 ... 1.000 ... 0.85 . . . . . . . 0.65 (7.01 Spread)
6L90E: . . . . 4.03 . . . . 2.36 . . . . . . . . . 1.53 . . . . 1.15 . . . . . . . 0.85 . . . . . 0.67 (6.01 Spread)
4L60E: . . . . . . . 3.06 . . . . . . . . . . 1.63 . . . . . . . . . . . . 1.000 . . . . . . . 0.70 (4.43 Spread)

OK, now multiply by a 'reasonable' axle ratio (the often forgotten step!)
10L80 x 3.23: ... 15.15 ... 9.66 ... 6.95 ... 5.72 ... 4.91 ... 4.13 ... 3.231 ... 2.75 ... 2.23 ... 2.07 (7.32 Spread)
8L90E x 3.23: ... 14.73 ... 9.60 .... 6.72 .... 5.46 . . . . . . . 4.10 ... 3.231 ... 2.75 . . . . . . . 2.10 (7.01 Spread)
6L90E x 3.23: . . . . 13.02 . . . . 7.62 . . . . . . . . . 4.94 . . . . 3.71 . . . . . . . 2.75 . . . . . 2.16 (6.01 Spread)
4L60E x 3.23: . . . . . . . 9.88 . . . . . . . . . . 5.27 . . . . . . . . . . . . 3.231 . . . . . . . 2.25 (4.43 Spread)

If I knew how to better spread those numbers out for a more visually accurate representation, I would ...
Many more underdriven gears that have also gotten more assertive have noticeably improved city MpG (and acceleration).
BUT
Despite more underdriven gears, the final gear ('times') the axle gear, ain't never gonna be under 2 in a truck / suv.
Hence lean cruise, followed by Engine Half@$$, followed by Cylinder Confusion, and yet highway MpG improves, but not as much.

Note:
3.23 is a decent axle gear for a 10L80, an 8L90 (does GM even bother to offer any other axle gear?)
3.23 is passably inoffensive for a 6L80 (although GM offered 3.42, 3.73, and rarely 4.10)
it sucks chapped @$$ for a 4L60E (which explains why even GM offered 3.42, 3.73, and 4.10 far more often back then).

Thanks for that. You certainly filled some big holes.

I did forget the axle ratio part. My 2024 has a 3.23 axle and my 2002 has the 3.42 axle... with the 4L60-E really going into 0.7 ratio as early as 45-50mph, that sparked my thoughts.. I know all early 4 speeds from the late 80s and on pretty much did this and the engine had to lug through it. The older big/small blocks were really good at this as the torque band was really on the lower side. (My 3-speed auto (no OD!) big block pickup still gets about 13mpg on the highway... and it is 45 year old technology!)

I do hope they really take advantage of what is possible with having 10 speeds....

 

[WalleyeMikeIII]

Many States require such labeling, but some do not. Patrick De Haan from GasBuddy tells us which ones don't:

Does your state require ethanol labeling? - GasBuddy

It's a fact that many know about ethanol- it contains less energy than conventional gasoline, and results in lower fuel efficiency. Some states have moved

www.gasbuddy.com

Spoiler: California, District of Columbia, Hawaii, Indiana, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Missouri, New Jersey, New Mexico, North Carolina, and Ohio

Gas Buddy indeed says MN not required to label, but my experience here is opposite. Furthermore, the law requires 10% biofuel (as an oxygenate) in all gasoline sold at retail for on road use (All fuel sold in MN for on road use must be "Oxygenated Gasoline") and further restricts to an ethanol content of 9.2-10%.
Almost all stations label whether it contains Ethanol, and How much, and they definitely label if it does not contain ethanol ("Non Oxygenated" fuel here is, by law, only usable in vehicles not designed for it, off road vehicles, boats, and small engines, and must be minimum 91 octane.) It is not dyed, however, so not sure how exactly they can enforce it. This sometimes leaves one in a lurch to either choose to violate the 'Oxygenated Fuel' law or put lower octane than required in a vehicle, since often the ethanol free is the only 'premium' available at a station.

 

[Marky Dissod]

Forgetting to multiply the gearbox ratios by the axle(s) ratio always creates problems.
Also keep in mind that, from the 70s til the noughties,
axle ratios for vehicles under about 7000lb were artificially pressured by CAFE MpG scores to be lower than desired.

Speaking in terms of GMTs weighing 5000lb or more:
4L60E with anything under 3.73 wastes fuel AND sacrifices gearbox durability / longevity.
6L80E with anything under 3.42 wastes fuel AND sacrifices gearbox durability / longevity.

I do hope they really take advantage of what is possible with 10 speeds ...

NO, YOU DO NOT - at least, not the way automakers are going to take advantage.

*Prepare for turbo-3-inlines to replace 4-inlines, turbo-4-inlines to replace V6s, (V6s will be replaced by 6-inlines),
twin turbo-6-inlines to replace most light-duty / passenger V8s (Stellantis Hurricane turbo-6-inlines killed Hemi V8s),
larger twin turbo-V8s will be EXCLUSIVELY for 2500-&-up work trucks and commercial vehicles,
smaller twin-turbo V8s will compete with larger twin turbo 6-inlines for ne-plus-ultra-luxe-high-performance cars
(twin-turbo V8s are already pretty much done killing V10s & V12s)

Also, due to more 8- 9- & 10-speed transmissions and more turbos,
Variable Valve Timing will look more and more like the Atkinson Cycle, with torque peaking OVER 4200RpM.

 

[viven44]

4L60E with anything under 3.73 wastes fuel

Agreed on the longevity.. no doubts there. Are you talking about city or highway cruising mpg ? Why would a 3.42 not fare better on highway ? For city, I could agree…

And all that Turbo future is scary (from a service standpoint).. maybe I’m used to working on simple things. Glad I started collecting engines/transmissions from wrecked trucks and parts trucks to keep my “fleet” going.

 

[Marky Dissod]

6L80 8L90 & 10L80 prove that 4L60 was effectively wasting fuel in metro/urban stop'n'go ...
GM almost always used 4L60's axle gear to bias the tradeoff toward highway MpG, sacrificing city MpG.
If we use the axle to bias the tradeoff toward city MpG, we sacrifice some highway MpG.

8L90E x 3.23: ... 14.73 ... 9.60 .... 6.72 .... 5.46 . . . . . . . 4.10 ... 3.231 ... 2.75 . . . . . . . 2.10 (7.01 Spread)
4L60E x 3.42: . . . . . . . 10.47 . . . . . . . . . 5.58 . . . . . . . . . . . . 3.42 . . . . . . . . 2.39 (4.43 Spread)
4L60E x 4.10: . . . . . 12.55 . . . . . . . 6.68 . . . . . . . . . . . 4.10 . . . . . . . . 2.86 (4.43 Spread)

Hopefully turbos get better thermal maintenance / longevity - otherwise turbos will NEVER last as long as their engines ...
especially if 4s & 6s start screwing with Cylinder Confusion ...

 

[Big Mama]

You number guys are awesome but way over my head. I just got a 23 Sierra Denali with the 10 speed. Longevity remains to be seen since they’re relatively new. From a seat of the pants perspective I can say the 10 speed it much more responsive than my 07 Yukon Denali. I find myself wanting to hit the gas more often due to this.
I wonder if that has anything to do with real world mpg vs calculated EPA numbers.
The mpg in the Sierra is almost 50% higher than the Yukon.

 

[viven44]

The low-end response I must admit is quite good on the 2024... I haven't driven it much yet since we bought it, but that was my recollection the day of purchase.

Wife is a very conservative drive. Per wife just now...

Our 2024 4x4 with the 3.23 axle gets 15mpg city / 19-20mpg highway... hoping this improves after the break-in period based on previous comments on this thread.

Our 2018 with the 3.42 axle (Tow pkg) 4x2 was used mostly on highway.... we got ~14 mpg city but highway is where it really did wonderful >=26mpg highway. Wife consistently challenged herself to get better highway mpg, and claims to have got even 29mpg during one trip... To be fair we never double checked the mpg indicator with manual calculations. And I must say the 2018 impressed us so much that we stuck with the GM brand for the next purchase. (We lost the AC condenser .. the usual leak on the weld... but I was able to replace that easily... R1234yf was the most expensive part of all that....)

The 2002 Yukon 4x2 I got recently with the 3.42 axle got about 13 mpg city at the most recent fill up.. I keep a close eye on the gas guzzlers I drive no idea on highway as I haven't had to drive much highway.

 

[viven44]

Towed 8200# yesterday with empty trailer weighing 2200#

Averaged 16.5mpg with empty trailer and 12.4mpg with load .. drove conservatively in tow mode 55mph and no higher than 60mph as it started fishtailing

 

[Marky Dissod]

Towed 8200# yesterday with empty trailer weighing 2200lb
Averaged 16.5mpg with empty trailer and 12.4mpg with load ... drove conservatively in tow mode 55mph and no higher than 60mph as it started fishtailing

I'm almost sure that more axle gear would neither improve the 12.4MpG-towing, nor the 16.5MpG-unladen ... the only thing GM can possibly do to the 10speed is improve the ratios relative to each other; 10 speeds seems like more than enough.

Are you talking about city or highway cruising MpG? Why would 3.42 not fare better on highway? For city, I could agree ...

Unladen, with 3.42, it depend on how fast you prefer to cruise on the highway, because at a certain point, 4th gear can't put enough power through the tires to maintain speed against drag.
Laden / city, it should be obvious that 4.10 gives the 4L60E a chance to spend more time in 3rd or 4th,
and less time in 2nd.

 

[strutaeng]

Towed 8200# yesterday with empty trailer weighing 2200#

Averaged 16.5mpg with empty trailer and 12.4mpg with load .. drove conservatively in tow mode 55mph and no higher than 60mph as it started fishtailing

View attachment 442144

Nice. What's the story with the Ford truck? Is that an F250?

 

[vcode]

Towed 8200# yesterday with empty trailer weighing 2200#

Averaged 16.5mpg with empty trailer and 12.4mpg with load .. drove conservatively in tow mode 55mph and no higher than 60mph as it started fishtailing

View attachment 442144

Good thing I don't live in Texas. I'd have a yard full of vehicles!