You may have heard the old saying that you should keep your gas tank at least half full, especially in winter when the temperature dips below zero.
There are arguments both for and against this practice, and your location and driving habits will likely dictate what you will ultimately do.
It's true that the "old days" it was important to never let your tank get lower than half full. That's because colder temperatures can cause condensation to form in the area of your gas tank that's not filled with gas. The water droplets that form are heavier than the gas so they sink to the bottom of your tank. This is where problems can arise.
Allowing your gas level to fall below half full in winter can cause corrosion in the tank (if it's metal). If the water freezes it can block the fuel line so the gas can't get into the engine. Condensation can keep your car's air pump from staying cool, which can damage the air pump. Vehicles nowadays have sealed fuel injection systems but condensation can still occur when there's more air in your tank.
Fuel pump failure can also occur when fuel is low because it sucks in air, causing your fuel pump to wear out, resulting in a hefty repair bill.
In addition to the possibility of causing damage or preventing your car from starting, letting your tank from below half full can also affect your car safety. If you stall out or get stranded in winter, which can happen on a slippery or snowy highway where cars backed up for miles, you could end up waiting hours for traffic to start moving again. Having a full tank of gas will keep your from running out of gas and having to be towed, or worse, yet, from freezing.