This Common Fueling Habit Could Cost You An Expensive Repair

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Many drivers have bad habits that can cause problems with their vehicles. These include not changing your oil regularly, accelerating and braking sharply, revving your engine for a quick warmup, and taking corners too fast. While these are  some of the common bad driving habits that are wasting your money, you can also cause problems by topping off your gas tank. If you want to go longer between fill-ups, you might be tempted to squeeze every bit of gas you can into your tank. Topping off your gas tank is a mistake because it can damage a part all modern gas-fueled cars have.

The fuel system in a car has a fixed capacity that’s limited by the size of the tank and related components like fuel lines, pumps, and something called an evaporative (or charcoal)  canister. This is a plastic housing with an activated charcoal filter element inside; dedicated lines carry gasoline vapors from the tank to the canister and then to the engine where they’re combusted.  Gasoline in liquid or vapor form expands with heat, and overfilling can overwhelm your evaporative canister, preventing it from working properly.  Your car’s check engine light might come on, performance will suffer, and you might even notice the smell of gasoline from inside the car.

The charcoal canister in your car has a pressure-sensitive purge valve that opens when it’s time to feed gas vapors from the canister into the engine. The purge valve won’t open when you top off your tank, though; it relies on vacuum pressure that doesn’t build up unless the engine is running.

The charcoal canister can flood when you top off your tank (you’re actually forcing gas into the filler neck and canister). You might be able to get away with this once or twice, but fuel will saturate the charcoal element after repeated top-offs.

Not only will this reduce the canister’s ability to capture and shed gasoline vapors, but your car might start to display a few symptoms that mimic other issues like bad spark plugs or a faulty catalytic converter. If your car’s performance and fuel economy drop, the engine idles roughly, or the cabin and/or exhaust smell like gas, it might be time to replace your charcoal canister.

You might want a mechanic to confirm this diagnosis, but replacing your own charcoal canister is a manageable DIY project on many cars. Prices for a replacement can vary widely by vehicle, though.  For example, a new canister for a 2001 Toyota Highlander with a V6 engine can cost nearly $600, while you can get one for the same year Nissan Pathfinder V6 from Amazon for $148.29. If you have the job done at a shop expect to pay 1-3 hours labor (usually between $90-$130/hr) plus a small markup on parts.