When using a vehicle that uses the standard fuel can item for fuel, the rate at which fuel is consumed is heavily dependant on vehicle speed, and this speed at which it outspeeds the refueling process is as slow as walking pace.

When tested on the German halftrack and the Panzer II, if I moved the vehicle any faster than a crawl, the fuel would consume at such a high rate that my tank would be empty in less than 30 blocks.

The testing was done with both a V8 and a Rotary Engine.

This is extremely easy to reproduce, merely spawn in seemingly any German vehicle in survival, add the fuel can items to inventory, and then try to travel at any pace as fast or faster than traveling by foot and watch as you run out of gas in seconds.

Tested on the latest version of Flansmod and the WWII content addon, using the Curseforge Launcher.

I purposefully made a Github account Just so I can agree with you.
It's a major issue, In which I have tested every WW2 and Modern Vehicle, in which all of them suffer the same fate.
Yes, I used all engines possible per vehicle, in which my studies show that the Sd.Kfz.222 seems to be the best vehicle in terms of fuel consumption, But it still only made it an extra 30 blocks.