nul = this spawn { waitUntil { if !(alive _this) exitWith {}; if (fuel _this < 0.25) then { _this setFuel 1 }; false } };
This code works for multiple air and ground patrol vehicle but still have a error message. I hate to see them lol.
So to finish this.
Fixed version of original script (bug was that exitWith returned nil):
_nul = this spawn { waitUntil { if !(alive _this) exitWith {true}; if (fuel _this < 0.25) then { _this setFuel 1 }; sleep 60; false } };
Other possible variant:
_nul = this spawn {while {alive _this} do {_this setFuel 1; sleep 60;};};
Probably the best variant: