If you have auth on a vehicle you cannot take fuel out of the vehicle but can place fuel in, due to this mechanic you can steal the higher quality/stack amount of fuel from a vehicle.
IE steam truck with 40 coal in it, you have a plant fiber, you drag the plant fiber into the slot that has coal in it, you then get 20 coal, steam truck then has a plant fiber and 20 coal in the other slot, repeat again and you have 40 coal, it has 2 plant fiber.
If you have auth on a vehicle you cannot take fuel out of the vehicle but can place fuel in, due to this mechanic you can steal the higher quality/stack amount of fuel from a vehicle.
IE steam truck with 40 coal in it, you have a plant fiber, you drag the plant fiber into the slot that has coal in it, you then get 20 coal, steam truck then has a plant fiber and 20 coal in the other slot, repeat again and you have 40 coal, it has 2 plant fiber.