Here’s Why Confusing Diesel With Gas at the Pump Is a Problem

It can happen to anyone. Maybe you were distracted by a text message or phone call or someone else pulling up at the pump. You grabbed the wrong handle, and now your gas tank is loaded with diesel fuel—a simple mistake that can cost you big-time.

The issue is combustion. Gasoline-powered cars have engines that run on a combination of liquid fuel and ordinary air, which are mixed together inside the vehicle and make their way to a cylinder block, where the fuel-air mix is compressed by pistons. A spark ignites the substance in a small, contained explosion; the gas produced as a result pushes back against the pistons, forcing them down and generating the power necessary to keep the car running.

But these engines can’t combust diesel. Unlike gasoline, diesel doesn’t readily mix with air unless certain conditions are met. While gasoline can evaporate at room temperature, diesel must be exposed to intense heat to follow suit. Diesel engines work by spraying the fuel into a cylinder that’s already filled with high-temperature compressed air, which makes the diesel itself combust spontaneously—no spark required. Gasoline engines can’t provide diesel with the temperatures it needs to combust, and, because it’s unable to evaporate sufficiently, diesel won’t ignite when the spark is released.

What to Do If You Put Diesel in a Gas-Powered Car

To those who drive gas-powered vehicles, diesel is useless. Ideally, you realized your mistake at the gas station before the car was even started—but if not, as soon as the last drops of gasoline in the car, truck, or motorcycle’s system are gone, the vehicle will shut down, leaving you stranded. And because gas-powered rides aren’t able to process the fuel, the diesel has to be removed manually—a process that isn’t cheap.

First, you’ll need to call a tow truck; then it’s time to enlist a skilled car mechanic. Depending on how much of the liquid you’ve poured into the tank, there’s a good to fair chance that some of it made its way into the car’s fuel line. Your mechanic will probably have no choice but to drain the entire fuel system, which can set you back $500 to $1000.

Gas stations try to stop their customers from making this mistake in the first place. Often, the nozzles on diesel pumps are designed to be too wide to slot into most gas tanks. Also, at many locales, these pumps are colored bright green, yellow, or orange, which makes them more conspicuous and serves as a visual reminder that they are not, in fact, gasoline dispensers. However, there isn’t a universal chromatic system. A few companies—like BP—use green-tipped pumps on their gas dispensers. So before you use any pump at any gas station, do yourself a favor and read the label.

A version of this story originally ran in 2017; it has been updated for 2023.