Should You Top Off Your Car’s Gas Tank?

Squeezing in that extra bit could be doing more damage to your car’s system than it’s worth

Person putting gas in their gas tank. Photo: Koonsiri Boonnak/iStock

Whether we want to round up or simply get as much gas into the tank as possible, some of us top off our vehicles by squeezing in a little more, even after the pump shuts off to indicate the tank is full. Can adding that extra bit of fuel damage components in your car’s fuel system?

“There’s a lot more going on in a car’s fuel tank than just a tank,” says John Ibbotson, Consumer Reports’ chief mechanic. “Fuel systems have become more sophisticated over time to keep up with increasingly stricter emission laws.”

Topping off could damage the onboard refueling vapor recovery (ORVR) system, a charcoal canister that collects potentially harmful fuel vapor during the refueling process and then absorbs it using activated carbon. The ORVR helps reduce hydrocarbon emissions by about 95 percent during refueling, according to the automotive supplier Eaton.

Adding more fuel after the gas pump clicks off can damage the charcoal canister by saturating it with fuel and cause the check engine light to illuminate. If the ORVR is damaged, it won’t adequately capture those harmful vapors. The system typically lasts the lifetime of a car, but topping off could lead to an avoidable repair that could cost hundreds of dollars.

Something else to keep in mind is that topping off your tank could cause gas to spill on the ground, which is a safety and environmental hazard. 

The bottom line is that topping off your car is dangerous to you and your car, and may cause problems. Your best bet is to stop pumping when the fuel pump clicks off.