Don't gamble with your gas tank: Why going below a quarter tank can cost more than a fill-up

How much gas is in your car's fuel tank right now?

If you fueled up on Wednesday or Thursday, the two most popular days to hit the gas station, your gauge might be sitting at half a tank or below. And with the price of a gallon of regular going for upwards of $4 nationwide, you may be tempted to stretch each tank further and let that needle drop ever lower than you did a few months ago.

Don't, warns David Bennett, the manager of repair systems for AAA. Letting your car get below an eighth of a tank increases the odds you'll damage your fuel system. To be on the safe side, refill by the time you're down to a quarter tank.

With gas prices averaging upwards of $4 nationwide, it may be tempting to go as long as possible between fill-ups. But then you run the risk messing up your fuel pump and filter, incurring a much bigger expense.

Each time you fill your car's gas tank, you end up adding some particulates and sediment that settle at the bottom of your tank, he explains. (This is even more important if you tend to buy cheaper gas rather than top-tier brands with more detergents and corrosion inhibitors that help extend the life of your car's engine.)

"If you run the gas too low, you have the opportunity to pick up some of that sediment into your fuel system, which could then clog up your fuel filter." Worse yet, Bennett says, "It could clog your fuel injectors. And that would cause engine performance problems."

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So what's involved in fixing your mistake?

"Typically you would need to replace your fuel filter, which is not that expensive," he says. "But the next thing that you may have to do is actually do a fuel injection cleaning."

All together it could cost around $250 by the time the repair shop cleans your fuel line, filters and injectors, Bennett estimates.

So when do you need to fill up?

"It's really once it gets down to maybe an eighth of a tank or a little bit lower and your light flashes" that drivers get into trouble and risk scraping sediment off the bottom of their fuel tanks, Bennett says.

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Better ways to stretch your gas money

► Fill up more often than once a week. Although Bennett recommends filling up once your car gets to a quarter of a tank, that doesn't mean you have to fill it all the way to the top every time. "Fill it another quarter or half" as a way to avoid constant sticker shock, he suggests. "Let's face it: Those gauges are not always accurate."

► Watch your tire pressure like a hawk. "Tire pressure is the biggest thing if you want to save," he says. "If your tires are low, you could decrease your gas mileage by about 5 mpg (per gallon)." Make sure you're using the numbers listed on the inside of your driver's side door jamb instead of the ones on your tires, he adds.

If you want to ensure that you're getting the most miles per gallon, make sure your tires are properly inflated. And use the numbers printed on the inside of the driver's side door jamb, not the ones on your tires' sidewalls.

► Clean out your car. "Reduce weight from the vehicle," Bennett suggests. Get the junk out of your trunk or hatch. And "if you have one of those luggage carriers, take it off until you're ready to take that trip." Studies by Consumer Reports and the Berkeley National Laboratory found that empty roof racks exact a heavy toll on fuel economy. How bad? You could be paying up to 25% more in gas, the Berkeley Lab said in a 2016 article in the journal Energy Policy

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