You never, ever fill up your tank before it’s almost empty. And when the fuel light comes on in your Kia Sorento, you don’t bat an eye. You know you can go exactly 40 miles before running out of gas. Just think — over a lifetime of waiting until the last possible minute to fill up your car, you’re probably saving hundreds of hours compared to the chumps who always keep the tank half full.

But is driving with the tank on empty really a good idea? What does it do to your car?

How Driving on Empty can Damage Your Car

Your dad may have told you that if you let the fuel light come on, the fuel pump will suck up water, rust, and dirt at the bottom of the tank. This used to be true, but is less likely in newer vehicles. Until the late 1980s, water would often condense on the walls of metal fuel tanks when they were more than half-empty, dripping into the gas. Modern fuel tanks, however, are usually made from polyethylene, preventing condensation and rust.

It’s still bad for your car to let the gas light come on, however. Gasoline serves to cool and lubricate the motor of the fuel pump, which moves fuel from the tank to the engine. “If you run the car low on fuel consistently, you can wear out the fuel pump prematurely, over-stressing it and making it hotter,” the fuel experts at Bell Performance explain.

If you notice your engine sputtering at highway speeds or surging forward unexpectedly, or if your vehicle begins to struggle when climbing hills or hauling heavy loads, that could be a sign that your fuel pump is going bad. It typically costs between $425 and $658 to replace the fuel pump, RepairPal says, depending on the make and model of your car.

Three More Reasons Not to Drive on Empty

1. In an emergency, you’ll be screwed – The alien mothership has landed in Los Angeles — on top of LA, to be precise — and everyone is getting the heck out of town. Except you. You drove home on empty instead of filling up the tank, and now you’re stuck. There’s nothing left to do but sit on your porch and offer the pod people a beer. Seriously, though: If your gas tank is empty, and your area experiences a major hurricane/tornado/earthquake/flood, you’ll be helpless. That’s why emergency preparedness experts say you should always keep the tank at least half full.
2. Gas gauges aren’t’ always accurate – Even in newer cars, the gas gauge gives you a fuzzy idea of how much fuel remains in the tank. Oddly enough, carmakers do this on purpose! Not only do people like having a little extra gas after the fuel light comes on, but they also don’t like seeing the needle drop down from F too quickly after leaving the gas station. So engineers have designed the gas gauge to hang out at F for a while, and show E long before the gas actually runs out. The upshot is: You can’t totally trust your fuel light. Even if you’ve done your research and you know how many miles you can go after the gas light comes on (from 30 for a Hyundai Elantra to 104 in a Nissan Versa), you can’t be sure you won’t run out of gas.
3. Running out of gas can be dangerous – Letting your car run out of gas completely can damage the car, but even worse, it can put you in grave danger. People have been killed by passing cars after running out of gas on a busy highway and even killed by their own car while trying to push it. A Texas college student was stranded in the desert for five days after her car ran out of gas near the Grand Canyon. Fortunately, she was rescued after she trekked 11 miles in a quest to find cell service.Our best advice: Just fill up the tank! But if you know you’ll never, ever give up the habit of driving low on gas, maybe it’s time to upgrade to car insurance that includes roadside assistance, just in case. Find the best deals on car insurance by getting customized quotes on Compare.com.