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Auto | Maintaining Your Car
Is it Bad to Top Off Your Gas Tank?


In today’s economy, gas prices seem to be on a roller coaster ride, skyrocketing one week before leveling out or dropping slightly the next. Retail gas prices have risen steadily across 2021 and then suddenly in 2022 as demand surged and energy uncertainty gripped economies in the wake of Russia’s invasion of Ukraine.

As consumers, it can be difficult to make sense of these peaks and valleys in pricing, so we may think it’s smart to reduce trips to the pump by cramming as much precious fuel into our vehicles as we can, but is jamming a vehicle’s gas tank as full as possible really the best way to save on gas? Does topping off do more harm than good? In this article, we’ll look at some of the facts behind topping off your tank and discover why drivers should avoid the habit of topping off their tanks.
Gas Pump Shut Offs Exist For A Reason
Although it may seem like the gas pump clicks off prematurely because you just know your vehicle can take another gallon or two or maybe you really want to get your total to an even dollar amount, the reality is that automatic shut offs on gas pumps exist for many good reasons. The main reason is to protect the consumer, the gas station, and the environment from the hazards caused by spilled gasoline and escaped vapors.

Not only is gasoline a hazardous material due to its incredibly flammable nature, but gas evaporates quickly, producing harmful vapors that contribute to poor air quality.

When spilled on the ground as consumers try to squeeze that last little bit of gas into their tanks, it creates toxic sewage runoff.

Because of these safety and environmental concerns, gas stations are obligated by government regulations to equip their pumps with vapor recovery systems that prevent vapors from escaping and fuel from spilling on the ground. This means that any gas you pump after your pump clicks off can wind up being drawn back into the station’s storage tanks, meaning you’re paying for gas that’s not going into your vehicle.
Topping Off Your Tank Is Bad For Your Vehicle
As previously mentioned, gasoline is highly flammable and evaporates quickly when exposed to heat. This means that even inside your gas tank, there is always a pocket of vaporized fuel that the vehicle’s Onboard Refueling Vapor Recovery (ORVR) helps manage and harness.

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Typically lasting for the life of your vehicle, the ORVR consists of a charcoal-lined canister that collects fuel vapor and absorbs it with activated carbon, effectively reducing hydrocarbon emissions during refueling by about 95%. All cars sold since 1971 are equipped with these closed-circuit systems that don’t just prevent polluting vapors from escaping, but they also help trap and burn fumes as useable fuel.

By topping off your gas tank even once, you run the risk of filling it to the point that the delicate charcoal filters in the vapor recovery system will become saturated in liquid fuel, ruining their capacity to filter vapors. Not only does this make your vehicle emit more hazardous emissions, but it can also impact engine performance and cause a reduction in mileage per gallon. Eventually, it may even lead to a costly repair that was completely avoidable.

While it may be tempting and we may feel like we’re getting away with longer trips between the pump, there are far better ways to save on gas and become a safer driver in the process. In the end, no matter which way you slice it, topping off your gas tank is a bad idea for all the following reasons:

  • Spilled gasoline and escaped vapors are environmentally harmful
  • Overfilling saturates your vehicle’s vapor recovery system which can lead to permanent damage and avoidable repairs
  • Gas stations are equipped with vapor recovery systems that recover gas pumped after the automatic shutoff. Topping off means you’re paying for gas that’s going back into the station’s tanks.