Fuel efficiency drop in newer models ?

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.

Assuming engines are the same size and AFM/DFM work the same (though they say DFM is much better) it seems like it comes down to the final gear ratio but may have other factors like tire size and the weight of the rigs.

The MPG you got with your 2018 is incredible. The highest estimate I could find was 22MPG hwy and 15 city. Your new rig weighs a little more but not enough to make such a dramatic difference.

My interest is piqued too so I’ll be watching this thread. Folks much smarter than me that have other explanations will chime in.

In calm conditions (no wind), flat ground, 65MPH, I routinely get 21-22MPG on highway in my 22 XL Denali. Wind, heavy foot, etc, will decrease it..

CAFE requirements have probably driven new calibrations "for cleaner exhaust" that is usually achieved by burning more fuel and incorporating timing changes (it's absurd, but true). I'm sure there is additional weight on these newer vehicles due to increased crash protection requirements. And, also the vehicle itself has grown in size. These would be my reasonings - right, wrong, or unpopular

WalleyeMikeIII said:

In calm conditions (no wind), flat ground, 65MPH, I routinely get 21-22MPG on highway in my 22 XL Denali. Wind, heavy foot, etc, will decrease it..

Click to expand...

My Escalade with the 6.2L also can routinely get 20-22 mpg on the highway, and the BEST MPG which has never been reset since new currently shows 28.0 mpg (50 mile window). Seems like the OPs results should be better, I would not expect the heavier LWB to be that much less.

They're not getting any lighter, AND they're not lowering their drag coefficient or their drag area ...
Most of the features meant to improve MpG are fighting an uphill battle against vehicles that will not get any lighter,
and have not improved their drag coefficient or drag area by much.

It's still a 5500lb-6000lb, 19ft long box, with an exposed underbelly.

I recall when the new design came out there were many comments about decreased mileage. Our 2019 has impressed me with the mpg we get. Use mid grade or better gas and I don't baby that motor.

For those that may not fully appreciate it:
Multi-Port Fuel Injection happens during the intake stroke, mixing it with air before compression
Direct Fuel Injection injects fuel into the air during compression.

Point is, DI SHOULD be able to take MORE advantage of higher octane, compared to MPFI.
But if you use 89 or 91 or 93 in your DI V8, it should not only yield better MpG,
but also better Miles per DOLLAR.

Another thing to add is this: most new engines have a richer running break-in period from new. Based on miles and time. The calibration is set to this to help protect the motor, seat the rings, etc. After 5k you will probably see more realistic numbers.

Make sure you are performing manual calculations and not standing on a soap box 100% supported by what your display is providing.