This Is What Really Happens When You Put Diesel in a Gas Car

The damage on your car’s engine can be pretty severe.

Refueling car at gas station. Filling fuel.Krasula/Shutterstock

Accidentally putting diesel into a car that runs on gasoline doesn’t happen that often, but when it does it can do a lot of damage to your vehicle and your wallet.

First, if you’re worried this is going to happen to you, don’t be—it’s pretty hard to fill up your car with diesel if it takes gasoline. The nozzle on diesel pumps is typically bigger—so it won’t even fit in your gas tank—it’s normally green, and at a completely separate, clearly labeled pump. Put your phone away so you’re not distracted and check to see that everything looks normal before pumping your gas. To make sure you don’t run into any other costly car problems, check out these maintenance tips that will extend the life of your car.

To most people, diesel and gasoline might seem like similar substances—for all we know, they both come from a pump at a gas station—but they’re not. “Diesel is a much thicker substance than traditional gasoline and it is ignited by pressure rather than a spark-ignition,” says Jake McKenzie, Content Manager at Auto Accessories Garage. “Because of its thickness, even a small amount of diesel fuel in a gas vehicle can clog the engine’s fuel injectors, filters, and lines.” Here are weird car features you didn’t know you might have.

In the unlikely event that you did put diesel into your car and you notice your mistake before you start driving, make sure to never start the engine. Then, get your car towed to a body shop right away so they can pump out the diesel to empty the tank, flush the fuel system, and replace the fuel filters. “Time is of the essence. Even if you don’t drive the vehicle, diesel fuel in the tank will still begin to clog up the fuel system, engine, and injectors,” says McKenzie. This will likely set you back around $400 to $500.

If you do start driving your car with diesel in it, you won’t get very far. A gas engine isn’t able to combust diesel fuel, so your car will move a few miles, make some strange noises, and then come to a stop. McKenzie says it will cause “incredibly costly cylinder and timing issues” in your car’s engine. This type of damage could easily cost you about $4,000 to repair—sometimes up to $17,000, McKenzie says. In many cases, it can end up costing more than the value of your car. Next, read up on these signs that your car is about to die.

Morgan Cutolo
Morgan is the Assistant Digital Managing Editor at Reader’s Digest. She graduated from the University of New Hampshire in 2016 where she received her Bachelor of Arts in Journalism. When she’s not writing for rd.com or keeping the 650+ pieces of content our team produces every month organized, she likes watching HGTV, going on Target runs, and searching through Instagram to find new corgi accounts to follow.