The Reason Why the Gas Pump Nozzle Is Always Shutting Off on You

The gas pump nozzle's frequent shut offs are all about safety.
The gas pump nozzle's frequent shut offs are all about safety. / Virojt Changyencham/Moment/Getty Images

It’s a beautiful day. You’re out for a drive. Your fuel tank is getting low. You pull into a gas station and select some unleaded. Periodically, the gas pump stops working, switching off with a clunk. You start it again. It happens again. You sell your car. You start walking everywhere.

There’s actually a reason gas pumps have the annoying habit of shutting off for no obvious purpose. According to Jalopnik, it has to do with an abundance of caution.

Safety First

At the very tip of the gas nozzle is a shut-off sensor port. A hole is connected to a pipe inset inside the fuel nozzle. The pipe takes in air. If it stops being able to “breathe,” the resulting vacuum shuts off the flow of fuel to prevent gas from backing up. Thus, your refueling efforts are interrupted.

The hole can be blocked as the level of gas in your tank rises, or even if a little splash-back occurs. The liquid blocks the airflow, the pump stops, the obstruction is cleared, and the pump will resume once you depress the handle again.

It’s likely some cars are more prone to this than others. That’s because a shorter pipe leading from the fuel cap to the tank can get clogged more easily, where a longer pipe allows for better flow. If the fuel pump you’re using shoots out gas like a Super Soaker, then the shut-off sensor is at increased risk of being triggered. Fuel pump nozzles can also deteriorate over time, leading to an uneven distribution of gas and causing sensor port problems.

Tips for Keeping the Gas Flowing

In that case, you’d want to adjust the clip on the pump to slow down the flow rate. You can also stop squeezing the trigger so hard, or maybe adjust the nozzle tip so it has a little more breathing room.

If none of that works and the pump is still working in spurts, then it might be time to have a mechanic check the fuel tank for a clogged line. It could also be a vent valve failure, where the car's system for venting fumes is affected and causes air pressure to build up, which can prompt the pump to shut off.

While it’s certainly a nuisance, the end goal is to make sure gas station customers aren’t showered in gasoline. For that, the occasional clunk is worth tolerating.

Now that that question is answered, find out what all of the symbols on your car’s dashboard mean.

A version of this story ran in 2020; it has been updated for 2023.