Rather then take the risk of running out of gas and possibly causing damage to the engine. Why not take the mfd or calculated avg mpg, at say with a quarter to an 1/8 of a tank to go. Fill it up and if it takes 12 gallons, you know you have 5.2 gallons left. Multiply 5.2 by what ever your mpg was, add it on to the odometer reading at the fillup. This gives an idea just how far one could have gone on a tankful, without the risk.

tjq