Wow. First the posted "MPG" means nothing. They don't do real world tests to come up with that number. It doesn't reflect actual "Miles Per Gallon." Miles Per Gallon are never constant. Who is driving, how they drive, where, and when all make a difference. The elevation you are driving at makes a difference. Also, running out of gas is bad for the car. There is probably a little amount of crud floating in the tank, as long as it never goes empty the crud never gets into the fuel system, but if it does go empty, that crud gets sucked down, so try never to go empty again. If you can't fix the fuel gauge and you know the size of the tank (18 gallons I think I saw) reset the trip odometer to 0 each time you fill up. Fill up the car when you estimate you've used a quarter tank. It should take just about 5 gallons. Use the actual number you get to estimate miles driven to a half tank. Verify several times you can somewhat accurately set a milage at approximately half a tank. 9 to 10 gallons of gas, max, each time you fill up. If, and only if, you can hit that 9 to 10 gallon mark EVERY time for like 5 times in a row of driving down to half a tank in mileage then (and only then) increase whatever your half-tank mileage is by 50%. This will theoretically get you to a quarter-tank. This number of miles is the absolute most you should ever drive without refilling. It gives you a 25% buffer which is solid and safe. You get to use 3/4th of your tank between fill-ups. Not bad without a working gauge. just remember you must always reset the trip odometer at fill up.