I have let the needle fall into the red - the "right" edge of the needle in the red. I have run it out completely - not recommended! The needle was deep into the red but not a good idea for many reasons. Keep the water out (good filter, drain the water separator if you still have it hooked into the lines and letting the needle tickle the red should not be a problem. If I am going to put fuel in the car I might as well fill it it up!