A fuel gauge doesn't often react incrrementally with any precision. You've driven 45 miles and you're expecting what type of deviation in the gauge from the 3/4 mark? You've never filled it? I don't know that you have issues or NOT but it would seem you don't either with just 5 gal purchases at random intervals! BG44K isn't going to hurt anything but the money maybe could be used for something more useful.
I don't know how to assume it's functioning accurately without a "fill up"! Fill it, set the tripometer, drive 100 miles, fill it, check mileage and fuel gauge level. Fill it, set tripometer, drive 150 miles, fill it, check mileage and fuel level gauge. You'll need to establish one (that it's full), two (some sort of expected mileage per gallon) and then evaluate the gauge with a more accurate set of "knowns".
Make a habit of fill ups and setting the tripometer, buy gas a regular calculate mileage intervals. You need to keep substantially more than 5 gals of fuel in the tank for sure. The fuel is the "coolant" for the fuel pump. If you want to buy lesser quanities of fuel at a time, determine the miles per gallon expected buy in larger than 5 gallon increments I believe and use the tripometer and not the gauge.
Advertised capacity is 20 gallons but it seems something nearer 18+ is the accepted norm.
Last edited by WVZR-1; 03-17-2013 at 10:51 AM.