Hello everyone,
This is going to be only marginally useful to most people, but someone asked about real fuel economy (and I'm trusting the car's calculations here). There is a 630ish mile run I do every year in December to drive from flatland Central VA to the Blue Ridge Mountains in NC to pick up a couple of Christmas trees. Just under half of the drive is just the car itself, then I hook up a 9x5 U-Haul utilitiy trailer and pick up a couple of trees and I drive back. Since I do this every year, I have some data points to compare...

I think the GL450 picture is from 2 years ago, rather than from last year. Mileage is VERY similar (had to take a detour this year because one road was out and in those parts alternative routes are few and far between) and weight would have also been comparable (fine, maybe I put on a few pounds). It looks like I managed a slightly higher average speed this year with the GLS, but I am surprised that, despite me being in Eco mode the whole time, fuel economy wasn't better than it was with the GL (which has a 7-speed gearbox and an Eco button that, I think, only turns on Stop-Start). Coupled with a smaller tank, that led to some range anxiety at the end - I usually fill up the car at the same time I pick up the trailer and then drive home in one go. The GL had just under 1/4 tank left, the GLS has 17 miles left, apparently. Costco is 8 miles away...

Some of that may be down to the larger wheels (23 vs 20), but still. I expected fuel economy to be better.

Yes, this is a very specific comparison, and the numbers will not mean much to most people, I was just very surprised that my real fuel economy on that trip wasn't at least on par, considering that the GL is now 8 years old and has 110k miles on it.


2015 GL

2024 GLS

 

I got about a 1 mpg improvement on the '23 GLS450 vs the '16 GL450 it replaced. As you noted, the older GL defaulted to ECO mode whereas the newer GLS defaults to Comfort mode.
This is based on manual calculation and not the car's reported fuel economy (which is known to be a good 1-2 mpg optimistic compared to manual calc).

 

I should have added that I'm not claiming scientific rigor. This is but one small data point, but since I do virtually the same trip every year, I was curious.

I had Eco on in the 2024 the whole time.

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For your comparison to be completely apples to apples, you would have to make the same rest stops, weather/temperature would have to be comparable, etc. There's just too much that could impact the results if conditions are not similar.
As I said before, if you are relying on the car's self-report for fuel economy, you can throw accuracy out the window!

I calculate fuel economy the same across all the different brands of cars I've driven:
1) Come to gas station and note the trip odometer mileage.
2) Once tank has been filled, note how many gallons were required at the pump.
3) Divide trip odometer mileage by gallons filled for mpg.
4) Reset trip odometer for the next gas fill.

Rinse and repeat! I never leave the car on while refilling on gas so there is no additional consumption that shouldn't be part of the calc!

 

The GasBuddy app is helpful for tracking MPGs manually.