My 2017 Golf Alltrack averaged 39.6 MPG on this monster 829-mile road trip, with near-constant AC use. It would have been over 40 MPG, but the last leg Vail to Denver got grindy with stop/go/slow traffic.
Occupant and luggage weight were low: it was just my son and I and maybe 25 pounds of stuff. Temperatures were in the 80-95° range, and roads were clear, and yes this is important because both affect MPG.
The biggest effect you’ll see on your fuel economy with road trips will be average speed. Over 55 or so MPH you’ll see it drop at the square to your speed, meaning your MPG at 110 MPH won’t be half of what you get at 55 MPH, it’ll be a quarter, roughly. On this trip my average speed was 49 MPH because most of the route was via state highways with a 55 MPH limit.
Why do so many posts here talk about fuel economy? It’s because MPG reveals a lot about engine health. If it drops, all other variables being equal, something’s wrong.
My Alltrack now has 69,9xx miles, and it’s on its 3rd set of tires, 2nd battery. I changed the oil most recently at 67,1xx miles.