Fuel efficiency drop in newer models ?

DocDoug said:

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

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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...

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.

WalleyeMikeIII said:

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...

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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.

viven44 said:

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.

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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%...

PPK_ said:

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%...

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

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


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

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

DocDoug said:

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

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Is this with the duramax engine?

viven44 said:

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

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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.

Marky Dissod said:

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).

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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....