Vehicle Gasoline Consumption

[PeacefulTreasure]

I just made my account for this, so it may already be known, it may not even be a bug, but I discovered something interesting earlier. 
While driving a vehicle using cruise control, you can accelerate without the cruise going off. I discovered that doing so until you hit the next higher gear, then letting the cruise take over again, would let your car maintain the set speed with a MUCH lower rpm. In the first image, you can see me maintaining 45 mph @ 2000 rpm. This corresponds to the black X in the last image. 
Pay close attention to the fuel gauge there.
The next image, and corresponding blue X, shows the moment where cruise control took over again, after I forced the vehicle up a gear. Rpm goes down to 1500, and this actually makes the vehicle a lot quieter, zombies don't notice it. However, fuel consumption skyrockets, which is pretty counter-intuitive to what you'd expect. I continued driving along that stretch of road to the Red X, my base entrace, where I stopped the car. Between the blue X and red X, my vehicle consumed an eighth of the entire tank, which is ludicrous. Doing this back and forth to the mall on the shortest path, will consume over 1/4 of the tank, while driving normally will only consume about 1/8th. This is... really interesting, and I'd like to find out why this happens, if it's a bug, or intentional. 

Edit: Just realized it'd be smart to include a link to the location on the map, I think  this will work.
https://map.projectzomboid.com/#0.9188361774299215,0.2836967108218473,76.67519984894946

Edited December 22, 2020 by PeacefulTreasure