I think it depends on the driving condition that you are going through. is it stop and go, hwy, etc. i try not to let it get to that stage, but if you do, when the light comes on i believe there should be 2 gallons left. they say the bad gas settles to the bottom so when you let it go to reserve it's pulls everything that settled to the bottom... anyways that's what i've been told and what i go by lol.
i'm sure someone will have a way better answer for you
