What Happens If You Put Gasoline In A Diesel Engine?

Can you put gasoline in a diesel engine or vice versa? It's the same fuel, right? Well, no and we'll explain here why you shouldn't mix gas and diesel.

Everyone fuels their car on a regular basis. Your awareness levels can drop on long car rides or hectic workday mornings. All it takes is grabbing the wrong nozzle at the gas station, and you’ve accidentally put the wrong fuel in your car!

Whether they admit it or not, many people have done this at some point.

But does it really matter if you mix and match? It’s all fuel, right? Won’t the gas pass through the engine harmlessly (or vice versa)?

In short, it’s badVery bad.

There are significant differences between diesel and gas. Let’s have a closer look at them now.

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What’s The Difference Between Diesel And Gasoline?

Crop hands crossing fuel nozzles

Diesel was named after its inventor, Rudolf Diesel, back in 1892. The fuel is made by refining crude oil.

While diesel used to have a high sulfur content, newer 2006 US laws only permit fuel with a very low sulfur percentage to be sold at gas stations.

Diesel fuel comprises larger hydrocarbon chains (molecules), so it’s much more dense and viscous than gasoline. As a result, it atomizes differently. Its flash point and autoignition temperatures are also significantly higher.

Given these, the opposite can also be said to be true. Gasoline is lighter and flashes at a lower temperature than diesel.

Diesel ignites using high compression. In contrast, gasoline needs a spark.

These differences in physical properties cause the resultant problems in engines and fuel systems when you fill up with the wrong fuel.

Gasoline

petrol gun with car

Gasoline, also called petrol(eum), is also made from crude oil. In big refineries, unfinished gasoline is prepared. It’s then blended to make it usable in our engines.

You can choose between up to three options at gas stations:

  • Regular (unleaded)
  • Midgrade (super)
  • Premium (super premium)

These grades are determined by the octane rating. In essence, the octane rating tells you how stable your fuel is — or the pressure at which a fuel auto-ignites.

The higher the octane rating, the more expensive the price, but the better the quality.

Can A Diesel Engine Run On Gas?

Let’s keep things simple here. No.

Diesel and gas might both be refined from crude oil, but they’re entirely different chemically. If you try to run a diesel engine with gasoline, you’ll break it.

So don’t.

Putting Gasoline In A Diesel Engine

diesel engine detail

So, what happens if you accidentally add gasoline to your diesel tank?

In short, you’ll end up with excessive engine knock and detonation. This is because gas ignites at much lower temperatures than diesel.

Your engine will not work at all eventually once it seizes and breaks. And it’ll most likely do this as soon as the remaining diesel is used up and the gas starts being pumped into the cylinders.

This is the serious one. Putting diesel in a gasoline engine messes the spark plugs up and can do severe damage. Still, it’s not as terminal as putting in a diesel engine. You’ll need to bleed the entire system (including the fuel tank, lines, and filter) – a costly and time-consuming task.

You might also need new injectors, and the pump should be checked.

In some cases, you might need a new engine – or a new car – altogether.

Damage To The Engine

It probably comes as no surprise that gasoline in your diesel engine can cause significant damage. Knock and detonation can cause a shock wave in your motor, damaging pistons, con rods, camshafts, crankshafts, etc.

Your fuel system may also be affected by the wrong type of fuel. The fuel pump, injector, and filters must be in perfect condition if they are to work. Gas breaks down the lubricating properties of diesel. In turn, this means the fuel filter doesn’t work correctly and gets damaged.

Adding gasoline to your tank may result in you having to replace the entire fuel system.

These severe side effects are a real problem and could be a car killer.

Unburned Fuel

Crop man refueling car on filling station

With all the knocking and detonation in your cylinders, the gas is burning at random times. This results in a large quantity being left unburnt.

You’ll see excessive black smoke pouring out the exhaust pipe.

This can also cause a problem with the DPF (Diesel Particulate Filter). The unburned gasoline starts to clog it up and can cause significant flow issues.

You’ll probably need to replace it entirely. That’s another extremely expensive mistake to make. A replacement DPF starts at around $1,500 and can rise to $3,000 or more.

Immediate Steps To Take

car technician holding the wrench

There are immediate steps you can take to prevent further damage.

Once you notice your error of adding the wrong fuel type, stop fuelling immediatelyCall a mechanic or road service support and talk to the staff at the gas station.

Most importantly, don’t start the car. You don’t know how much gasoline has mixed with the remaining diesel in your tank.

If your tank was almost empty, it means the gas will flow straight into your engine. Even if it was half full, you don’t know if the pump will force gas or diesel down the lines.

Once the tow truck arrives, go to a mechanic you trust. They will flush out the fuel from the tank and check if any parts of your vehicle got damaged.

A fuel system flush will set you back $400 – $1000, depending on the quantity of gas in your diesel motor. This is definitely a costly mistake to make. However, a new engine or a written-off car would be much more expensive.

Conclusion: What Happens When You Put Gas In A Diesel Engine

While accidents do always happen, you’re unlikely to get away with this one. Many may say a little bit of the wrong fuel in your tank doesn’t affect your car, but internally it’s like poison.

Keep your engine switched off after filling your diesel car with gas. It might literally save the vehicle’s life.

The high costs involved with flushing out your engine will make this an accident to avoid again at all costs. But, as the German poet Goethe once said, “By seeking and blundering, we learn.”

The best way to keep your costs down? Don’t put any gasoline in your diesel engine!

Drive safely!

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Benjamin Kitchen

Ben is an automotive author from England. With experience in a fast-fit garage, he's an IMI-qualified light vehicle technician. He aims to help drivers worldwide with common automotive problems. You’ll often find him working with his 1.2 Vauxhall Corsa – it may have a tiny engine, but in eight years it's never once let him down!

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