Left the garage to head to Home Depot (about 4 miles) with the gauge showing a 1/4 of a tank. About 3 miles in she stumbled and then the low fuel alert came on. Gauge still showed 1/8 of a tank. This is how much I put in at the nearest gas station. I suspect the gauge is bad. Any idea how many gallons she actually holds? Manual says approximately 21.6.