Thats true. I noticed that consumtion still remains 0.00 when very small amount of gas is aplied (also when idling). (Maybe you can combine data with gas pedal position.) That is the only fialure. Good job anyway and thanks for your sharing!
Choose tga format and save file. Than enable "Channels" view. Here you will see that Alpha1 channel is added. That channel is for transparency. So you have to copy your picture in that channel. Black color means full transparency and white means no transparency.