How far should you fill your fuel tank?

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The fuel you put in your tank is important - so how full should you fill it? Image from Flickr.

It seems relatively simple: your car needs fuel, so you add gas, E-85, diesel or biodiesel. There is a huge amount of debate, though, over exactly how full to fill your tank. Should you increase your gas mileage by filling it halfway? Or should you top it off, extending how long you can go between fill-ups as long as possible? What about somewhere between those two?

Halfway up – better mileage?

One school of thought argues that you should never fill your tank up all the way. The idea is that the weight of the fuel will weigh down the car and decrease your gas mileage. By only filling your tank halfway, you will supposedly increase you MPG. However, if you fill your tank only halfway, you have to fuel up your car twice as often, which could mean more driving around. Always running with a half-tank of fuel will save less than 100 pounds; in the end, it will save you five to 10 gallons of fuel per year.

Top it off – fewer trips?

On the opposite end of the fuel-tank fillers are those that top off the thank as full as it will go. “Topping off” is when you put additional fuel into the tank after the gas pump has automatically shut off. You may get a few extra miles out of your tank of gas each time, but is there any risk? In most vehicles, there is. In order to capture the fumes from evaporating gas, there is a filter on the gas cap. If you top off the tank, you are running the risk of overflowing that filter. The filter can cost several hundred dollars to replace and is required for a car to pass emissions tests.

Good fuel hygiene

Keeping your car running well and clean is important. The fuel your car runs on is just as important – so keep it clean. This means allowing your tank to run close to empty at least once every few months to keep settled gunk out of your tank. You should also ensure that you are always putting the octane of fuel in your tank that your manual calls for – not less.

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