I just bought a 2003 VW New Beetle. I filled it up and have driven 50 miles and the gauge is already down to half a tank. How can I test to see if it is the gauge that is not working properly or is there something wrong with the car.
Take the Bug down to the gas station and fill it up again. Keep careful check on the gallons as you refuel. If it takes around 2 gallons to fill it up…make an appointment with a good mechanic to have the gas gauge fixed. It might be a wire or it could be the float in the tank. I doubt that the Beetle is using a half of a tank of gas in 50 miles.
If you really filled it up and it’s down to half after 50 miles with out smoking or stuttering, you definitely have a defective gauge.
I would look in the OWNER’S MANUAL to find the tank capacity and do a rough calculation of how far you can go on 3/4 of a tank, and then just keep driving. Some gauges drop rapidly to 1/2 or so and then take forever to reach zero. If the bottom half of the scale works accurately, you don’t have to fix it.
Or leaking, although a leak of that magnitude should definitely be seeable and smellable.
I suspect that the vent system may be out (leading you to think you filled the tank when it is only partly full) or the gauge may be off. In either case you should have a better idea once you follow missileman’s advice and do check the fuel usage