What Happens If You Put Gas in a Diesel Engine?

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Hands reach and grab one of four fuel pumps at a gas station

If you don’t know what happens if you put gas in a diesel engine, trust us when we tell you it’s not good. This is one mistake that’s better to learn from others than experience yourself. 

Today, we’re sharing with you why you should check twice when grabbing the handle to fuel your vehicle. Let’s get started!

What Is the Difference Between Gas and Diesel?

Gasoline and diesel are both fuels that contain chemical energy, which is transferable into mechanical energy. This conversion takes place through explosions within both gas and diesel engines. However, how the explosions occur inside the engine varies based on the fuel source.

A gas engine uses a spark plug to ignite the fuel and compress it, leading to the explosion and creation of mechanical energy. Diesel engines don’t have spark plugs, igniting via extreme compression instead. This type of compression ignition will damage a gas engine.

Liquid diesel is thicker than liquid gasoline, making diesel more energy-dense so it can evaporate slower. These two characteristics allow diesel fuel to create more power and typically be more fuel-efficient than gasoline.

Hear one driver’s story of what happened when he put gasoline in his diesel engine.

Can You Put Gas into a Diesel Engine?

While gasoline is often cheaper than diesel at the pump, it won’t save you anything to put it in your gas tank. It will likely cause thousands in damage to your vehicle, and you’ll probably be calling a tow truck within a mile or two. 

By putting gas into your diesel tank, you instantly throw off the vehicle’s fuel molecular balance and reduce the fuel’s flashpoint. This can result in a premature ignition and cause massive damage to your vehicle.

Don’t turn on the vehicle if you fill up with gas instead of diesel. Call a tow truck to take your car to your favorite mechanic. Don’t risk driving your vehicle to the mechanic just to avoid a tow bill; it will result in a much larger repair bill.

A hand grabs to put diesel in their engine.

Pro Tip: We made these 10 beginner RV mistakes so you don’t have to →

What Happens When You Put Gas in a Diesel Engine?

A handful of things happen when you put gas in a diesel engine, and none of them are good. Let’s look at what exactly happens if you make this mistake!

The Flashpoint Changes

The second you put gas in a diesel engine, you change the fuel’s flashpoint (when the fuel ignites). As the gasoline mixes with the diesel in your fuel system, it creates an inconsistency in the flashpoint throughout the entire system. This can result in large pockets of gasoline in your system that can prematurely ignite and damage the engine.

Damage to the Fuel Pump and Diesel Injectors

Gas and diesel vary in the amount of lubrication they contain. A diesel engine’s fuel pump and diesel injectors rely on this lubrication for optimal performance. Diesel fuel has proper lubrication, but gasoline does not. This will damage these sensitive components and likely result in their needing replacement.

A motorhome with a diesel engine rolls downs a California highway

Incomplete Combustion

If you don’t catch your mistake at the pump and start driving, you’ll likely see excessive, thick black smoke spewing out of your tailpipe. This is incomplete combustion and results from the vehicle’s onboard computer system attempting to compensate for the lack of combustion by adjusting the fuel-air mixture.

The Computer Sensors Fail

As your vehicle attempts to adjust, you’ll lose power and performance, and the sensors can overheat and cause permanent damage. The computer sensors will also get a thick coating of soot and make it impossible to detect anything.

Pro Tip: Learn why these Class C diesel motorhomes are an excellent RV option.

What to Do If You Put Gas in a Diesel Engine

You can do a handful of things to avoid making a bad situation worse. Now that we know what happens if you put gas in a diesel engine let’s look at what you should do if you make that mistake.

Don’t Try to Start the Car (or Shut Off the Engine Immediately)

The best-case scenario is that you catch your mistake before starting your vehicle. It’s inconvenient to get stuck at the gas station while you figure out repairs, but it’s a much easier repair than if you were to start the vehicle. 

But if you don’t catch your mistake until after starting the engine or you’re driving down the road, pull over and turn the engine off immediately. This will minimize any further damage that might occur due to your mistake. 

Two campers pulled off on the side of the road with their RV to call a tow truck.

Call a Tow Truck

Immediately call a tow truck. You may reach out to your insurance company and see if they can arrange your tow and get the ball rolling on your future insurance claim. A tow truck can take an hour or more to arrive, especially if you’re driving a large truck or require unique accommodations.

Get to a Mechanic

Have your vehicle towed to an experienced mechanic capable of working on a diesel engine and who has experience with this type of mistake. You’re not the first person to make this mistake (and won’t be the last), and there are plenty of diesel mechanics that can help get you and your vehicle back on the road.

A repair of this magnitude takes time and can cost upwards of $10,000 to repair. Don’t expect it to be quick or cheap. This type of mistake typically results in an insurance claim and could cause your insurance premium to increase.

Check the Nozzle Before You Pump

Putting gas in your diesel engine is not a small mistake, but with a little attention, you can avoid making a costly mistake. Most diesel fuel pump handles are a bright green color. (Except at BP fuel stations. Some diesel owners avoid BP stations altogether for this very reason.) Regardless of color, all nozzles will be marked, so you can tell the difference. 

Making this mistake isn’t the end of the world, but it’ll cost you. Take your time at the pump, and you can save yourself from the stress and financial burden of a repair. 

Have you or someone you know ever made the mistake of filling up with gas instead of diesel?

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3 comments
  1. In the old days people talked about adding a little gas to the tank in very cold weather for easier starting. Does it work?
    I have no idea. At a little over 1/4 million miles on mine, I’ve never done it. Don’t intend to either..
    Either through luck or paying attention, I’ve never accidentally put gas in it.

  2. I know of two people who have put gas in their diesels. One was my brother and he filled up his tank and drove home. The other person was a friend who started putting gas in and realized his mistake after 4 gallons. He just filled it the rest of the way with diesel and all worked out.

  3. Happened to a neighbor’s truck when he loaned it out. Guy did him a favor and filled it with gas. Drove it a little before it stopped. After towing it to the mechanic, he said all you had to do is add a quart of oil. It’s an old Dodge I don’t know if it would work on a newer truck.

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