Will A Little Gas Hurt A Diesel Engine (Accidentally Mixing Gasoline And Diesel Fuel)

We’ve all been there. Gone to fill up, as you’ve done so many times before - but you forgot this vehicle is a diesel! 

You’re panicking - what can I do? Is my engine going to survive this? What are the next steps? Who do I call?

Will A Little Gas Hurt A Diesel Engine (Accidentally Mixing Gasoline And Diesel Fuel)

Don’t worry too much - let’s take a look at the effects of gas in a diesel engine and what you can do if you accidentally mix the two. 

The Differences Between A Gas And Diesel Engine 

Okay, so it’s first important to know the difference in how a gas engine and diesel engine works. 

The real difference lies with how the fuel converts into energy. In a normal gas engine, compressed air will become mixed with the gasoline.

After this, the spark plugs will create an ignition which can allow propulsion of the vehicle. 

Diesel however, the compression of air is the first step which heats the air - when the diesel is mixed with the heated air, an ignition is created. 

Another difference is the injection of these fuels. With gas engines, you can have either a carburetor or a PIS (port-injection-system.) Carburetors mix gas and air and then send that for compression in the cylinders.

A PIS will introduce air into the gasoline prior to intake. Diesel is sent straight to the cylinder. This also makes diesel engines far more energy efficient than gas. 

It’s also important to note that the engines for diesel vehicles generally have less parts (and therefore less parts that can break) because they don’t need certain components to work - like a spark plug. 

What’s The Difference With The Actual Fuel?

Gasoline is a much thinner form of crude oil when compared to diesel and therefore can evaporate much faster.

So, you might find you can go the extra mile with your diesel engine but it can cost an extra few bucks. 

What Happens If You Mix Gasoline and Diesel?

To put it simply - you’ll ruin the fuel pump. A diesel pump is greased by the diesel itself so if gas gets into the mix, the lubrication becomes lowered leading to metal/metal physicality and particles - totally damaging the insides!

If you ignite these fuels, you’ll make the problem worse. 

Will A Little Gas Hurt A Diesel Engine (Accidentally Mixing Gasoline And Diesel Fuel)

Even the smallest amount of gas mixed into a diesel engine can cause a serious issue. So the answer is YES - adding a little gas will indeed hurt a diesel engine.

But, What If I Do… What Should I Do?

This mistake is actually more common than people give credit for. Thousands of Americans every year opt for the wrong fuel by complete accident. There are steps to take though:

Don’t Panic

You won’t help anything or anyone by panicking. Chill out. Go grab a soda from the gas station and let’s think about this. 


Don’t ignite the fuels. Leave the car off. 

Call A Professional 

Got a number on your cell phone? Doesn’t matter. Walk into the gas station and they should be able to point you to a professional who can come and help.

If you’re in a precarious spot, they may even assist with moving your car out of the way (Remember, without the engine being on!) 

What Is The Process? - What The Professionals Will Do 

Assuming you’ve followed the above steps, a professional will be able to completely drain the fuel out of your system and then add some of the right fuel. This process can take around half an hour or so.

If you have turned on the engine, your system might need to be totally replaced. This is not cheap - so best to stick to the steps. It’ll also take much longer! 

How Do I Know It’s Been Misfuelled? 

There are some common signs if you’ve put gas in a diesel engine:

  • Loud noise from the car when hitting the gas
  • A smoky exhaust 
  • The car isn’t going as fast as normal 
  • The engine fails entirely 
  • Warnings appear on the dash 
  • Your vehicle will not restart

What Are The Costs Associated With Misfuelling?

If you’ve got insurance, it’s worth checking to see if you’re covered for misfuelling. They may also be able to provide assistance wherever you are. 

However, without insurance - the costs differ. You could be looking anywhere from 400-2000 dollars. It really depends on your car and the company/person you hire to help.

It may also cost more if you call out of hours, along with any other added expenses such as getting towed, extra fuel and cell phone calls. 

How Can I Make Sure I Don’t Put Gas In? 

Prevention is key. A good way is to put a reminder in your car or on the fuel cap. You could even write it on your keys in a keyring.

If you’re loaning somebody your car, make sure you tell them what fuel your car takes. 

I’m Interested - What Happens If I Put Diesel In A Gas Car Engine?

It’s actually not as serious as putting gas in your diesel.

The most common problem is that the spark plugs end up greased with diesel and sometimes your car might struggle to ignite the fuel. 

Even though it is less serious, it is still recommended to get professional assistance right away to ensure your vehicle doesn’t suffer long term as a result - or breakdown on the side of the highway! 

The Bottom Line 

The bottom line is that even a small portion of gas in a diesel engine will cause serious problems.

You should always remain focused at the gas station when filling up to make sure you’re not giving yourself a costly and time consuming problem. 

If you’re ever unsure as to what fuel you should be using, consult your vehicle’s manual, call the seller or manufacturer or even ask at the gas station.

It is always recommended to get good car insurance too, the extra monthly cost could save you thousands. 

I'm an environment and energy blogger who teaches outdoor and energy enthusiasts how to be better informed when it comes to purchasing or maintaining a generator, solar panel system, or anything else related to your energy needs.