Sometimes the gas light does not come on cause it just doesn't get run down enough. You don't want to go that low anyways, when it gets that low and you run it to fumes your fuel pump begins to suck all the shit off of the bottom of the tank. The stuff that never gets used which can than cause a backup. Also, when you fill up you want to go all the way too, I know sometimes $$$ is tight, but the same thing can happen to the top of the tank as well as the bottom. Sediment.