IDK if I've mentioned this in this thread in the past. However, my(98 hp/109 lb.ft) 1988 Honda Accord LX 2.0L/2bbl/4spd auto(EPA c:24/h:34) got consistently higher(~37 mpg) than any other vehicle we've owned including the (182 hp/180 lb.ft.)2015 Nissan Altima 2.5 SV(EPA c:27/h:38) that I currently own.
Yes, this newer Altima is ~700 lbs heavier, ~85 hp/70 lb.ft MORE POWERFUL. However, I just don't get the fuel economy out of the Altima as I had hoped. It's not bad but not as consistently higher as the older Accord was regularly. Since I don't actually do any city, stop & go/slow & go driving, I can get about 28-29 mpg combine. My EPA combined is 31.
And on the highway, it is closer to 34-35 mpg when traveling out of state and driving for several hours(6-8 hrs) from 1 tank to another. But, we usually have 2 passengers & luggage.
I have gotten over 40 mpg(calculated, not car computer) on a straight, flat drive with not much stuff so, it can be done. But if we travel through any hilly/mountainous highway, mpg drops.
As all new(er) vehicles are... this 2015 Altima is a 1000X better, more comfortable, quiet, better riding car than that '88 Accord ever was.
And as far as fuel economy, I do understand that YMMV. I am an easy driver who drives for good fuel economy.