I realize that this sounds silly, but hear me out:
My usual driving these days is a 320 mile high round trip across WV and Maryland. I've been pretty consistently getting around 35~ mpg round trip with this.
I usually get better mileage east than west, but I realized this is because the station I fill up there isn't level. There is a 500 foot elevation change from where I start to where I go but over 160 miles that's not an issue. When I get back it averages out so it's not that big of a deal.
Anyways, scangauge is usually correctly calibrated each tank fill. (Off by less than .1 gallon)
Recently though, my car was loaded up like this:
And I could really feel all that extra weight in my glides. I've driven this route so many times I know where to glide and where I can keep coasting down the next mountain, I know where to neutral coast versus in gear coast for DFCO, etc etc
But this changed it all. I could coast much much further than I could normally, and I could even DFCO on parts that before I couldn't maintain speed in neutral.
And to top it all, the engine didn't seem to notice, as at 55 or 60 (what I'm usually doing up the mountains) the engine still would maintain 16~20 mpg up. Then I could glide all the way back down. And then some.
Scangauge was actually reporting 38 mpg until I hit traffic near the city, it usually is reporting 36 until I hit traffic.
I understand that removing weight helps with the city, but how much does it really hurt on the highway, through the mountains?
I might do a mini experiment and throw some weights in the car and see how much farther it will coast.