Hello, so about the fuel system it all really depends on what you are using on the server as is.
Theres a bunch of fuel systems out there preset up. So its a easy install that would fix all your issues if your still having them. After searching and testing many different fuel systems for my server i decided to use this one.
And so far it works great with no issues and yes random car fuel when you get in a car for the first time.
https://forum.cfx.re/t/release-frfuel-v1-1-0/5467
Features
Fuel level synchronized between players vehicles
Vehicle’s dashboard shows actual fuel level
Randomized fuel level for NPC’s vehicles
RPM based fuel consumption
Vehicle max torque and acceleration has impact on overall fuel consumtion rate
Original fuel tank capacity for every vehicle, taken from handling
All gas stations that is in game are available
Events
Hope this helps if you still need help that is lol.