Pouring Gasoline in a Diesel Engine – What can happen?

Suppose you poured some gasoline into your engine. No big deal; sounds pretty normal. The only problem is that your car is a diesel.

You just poured gasoline into a diesel engine. What happens now? Is it gonna run? Is it gonna break down? Is it simply gonna explode?

No, in fact, it won’t explode. It will run, but only for a short time. But that’s not a good thing indeed. But what if you poured the gasoline into your diesel just to know what would happen? To answer in simple terms: if you pour gasoline into a diesel, it will be severely damaged, even if it can run for a while. Pouring diesel into a gasoline engine will do the same thing, except that gasoline in a diesel engine causes far greater damage.

But why does this damage the engine? Both are fuels. Both are by-products of oil. To answer this, we need to understand how these two types of engines, namely a gasoline engine and a diesel engine, work.

What if someone accidentally pours in gasoline in a diesel engine?

It won’t be pretty if you accidentally put gasoline into a diesel engine. The problem is that gasoline fuel is formulated to resist auto-ignition, which is not the case with diesel fuel. It’s impossible for a diesel car to burn gasoline. If it does manage to burn it, the detonation of the mixture will occur at irregular times. The pistons and piston arms are designed to withstand the fuel explosion if the explosion occurs in a timely manner. Gasoline in a diesel engine burns the fuel at irregular times and can, therefore, damage these parts.

Aside from that, gasoline can quickly destroy the fuel pump. The fuel pump of diesel fuel differs a little from gasoline because diesel also serves as a lubricant for the fuel pump. Gasoline causes the fuel pump to dry out, and without lubrication, the moving parts rub against each other and eventually fail, similar to the condition of an engine without any oil.

When the diesel engine is started, this causes the gasoline to circulate in the pipes and in the engine, causing sensitive parts to fail and the fuel pump to stop working. If, after you have filled the tank with the wrong fuel, you do NOT start your car, this can save you thousands of dollars for the replacement of damaged parts.

If you find that you have put petrol in your diesel engine, turn it off immediately and tow it to a mechanic’s workshop to replace the fuel.

Diesel-Gasoline comparison

At first glance, it would appear that the two types of engine, the gasoline engine and the diesel engine, work somewhat similarly. Both have pistons, cylinders, fuel lines, pressure lines, both require oil, and both burn a mixture of air and fuel to operate. Although both engine types are essentially the same, the main difference between the two is the method of ignition of the air-fuel mixture. This difference is all that distinguishes the two types of engines from each other. In addition to the difference in the engine, the difference is also in the two types of fuel.

Gasoline engines

Gasoline engines work in the same way as diesel engines, except that they use gasoline as fuel. The fuel is fed through the pressure lines and then into the engine. Depending on the fuel injection method, some cars use a carburetor to feed fuel to the engine, while modern cars today use electronic fuel injection technology. Gasoline engines have what we call the spark plugs to ignite the air-fuel mixture. Depending on the number of cylinders in an engine, there are 3 or more spark plugs. If a car is a V-8, there are 8 cylinders and 8 spark plugs for each of the cylinders. The timing belt makes the camshaft rotate so that each cylinder ignites the mixture at exactly the right time, so that the ignition of the fuel in each of the 8 cylinders is smooth and the engine remains in balance.

The key thing here is that gasoline engines rely on spark plugs to ignite the fuel. This is due to the compression ratio of gasoline. Once the gasoline is sufficiently compressed during a cycle, the mixture becomes hot enough and the spark plugs ignite quickly to ignite the mixture and produce the power.

Diesel engines

Here’s the thing: While most things in a diesel engine are the same as in a gasoline engine, diesel engines don’t have spark plugs. These engines do not need spark plugs to ignite the fuel. It is in this regard that the difference in fuel type is important. Diesel blocks use a compression ratio that is much higher than in petrol engines. It is basic knowledge that when compressed, air tends to heat up. Simply put, diesel is compressed much more than gasoline, which heats the fuel so much that the diesel ignites in the cylinders without the need for a spark plug.

This is also because diesel burns at a much higher temperature than gasoline, which is why diesel fuel cannot be ignited with spark plugs because the heat is too low. This causes the diesel engines to make this knocking sound when running because the diesel inside explodes at a higher temperature.

Diesel Fuel vs Gasoline Fuel

Both of these fuels are by-products of crude oil or petroleum. But a certain difference in chemical properties makes the two fuels different. Both of these fuels are hydrocarbon chains. The only difference is that diesel fuel contains more of them. This makes diesel less volatile than petrol, which means that diesel is not as easy to ignite.

A gasoline engine compresses gasoline at a ratio of 8:1, which can vary up to 12:1. A diesel engine, on the other hand, compresses the diesel fuel at a higher ratio of 14:1, which can vary up to 25:1. As a result, diesel-powered vehicles produce a much higher power output than petrol engines.

To avoid the mistake of filling up with the wrong fuel, the size of the filler necks for diesel fuel at the petrol pumps is larger than that for petrol, which makes it more difficult to fill diesel into petrol engines; but for the other way round, the problem remains.

Gasoline in a Diesel Car Symptoms

Since gasoline and diesel are two completely different types of fuel, you can get many symptoms if you have gasoline in your diesel vehicle. Here is a list of the most common symptoms that usually occur when you fill up your diesel engine with gasoline.

The most common symptoms of gasoline in diesel vehicles are knocking noises from the engine, rough idling and acceleration, engine warning light and the engine may stop and not start again. Never drive your car with gasoline in the diesel tank. Switch off your engine as soon as possible and tow it to a garage or to your home. Drain the petrol from the tank, replace the fuel filter, and fill it up with diesel again.

1. Check engine light

Since modern car engines are very intelligent, it often detects when you have put petrol in your diesel engine. This often leads to a check engine or service engine light appearing on the dashboard of your car.

2. Knocking sound from Engine

Since gasoline is much more flammable than diesel fuel, you can often get a loud “knocking” sound from your engine that was not there before. If you have only put a little petrol in your diesel tank, you may not hear the knocking sound, but it is a good sign to look out for if you suspect you have put petrol in your tank.

3. Rough idle and acceleration

You can often experience rough idling and rough acceleration when you have filled up your diesel tank with gasoline. This is because the engine is designed to run perfectly with diesel fuel, and diesel and petrol are two very different types of fuel.

4. Engine stops and won’t start

In many cases, if you have filled up a lot of fuel in your empty diesel tank, it may happen that your engine stops and cannot be started again. If this happens, it can lead to very expensive repairs if you are unlucky.

Will my diesel car get damaged by petrol in the fuel tank?

Yes, many parts can be damaged if you have too much fuel in your diesel tank. In many cases where you have a half tank of diesel and only add a little petrol, it will probably not cause much damage. However, since you often drive to the petrol station with an empty diesel tank and fill it up with petrol, it can cause serious damage to your engine and result in some very expensive repair costs.

As petrol does not have the same lubricating properties as diesel fuel, it can quickly cause serious damage to your diesel pump. A defective diesel pump can cause metal chips to come loose and fill your entire fuel system. If this happens, you will often need to replace the entire fuel system, including hoses and fuel lines.

It can also cause damage to the internal parts of your engine such as the pistons if you are very unlucky. This is quite rare, and most often only the diesel pump is damaged, resulting in metal chips throughout the fuel system.

What to do if I have petrol in my diesel car?

If you think you have gasoline in your diesel tank, the first thing to do is to stop your car in a safe place and turn off the engine as soon as possible. If you are sitting at the gas station and have not started your engine before realizing that you have filled it with the wrong fuel, do not start the car!

Towing the car to a garage or to your home. Drain the fuel from the tank either with a fuel hand pump or with the help of the suction pump built into the tank. If you have a main pump in the tank, you can lose the fuel pressure line and recycle the ignition to get the fuel out.

After you have got all the gasoline out of the tank, replace the fuel filter and fill the tank with diesel again. Then start your car and try again. In many cars, you will need to bleed the diesel system before you can start it.

If you follow these steps, you may be able to save the engine, and it will work in 90% of cases. In some cases, if you have driven too far with too much of the wrong fuel in the tank, your diesel pump may have been damaged, which can lead to a replacement of the entire fuel system, as the pump fills it with metal chips.

Conclusion

• Gasoline and diesel are two completely different fuel types, and you can get a lot of strange symptoms if you have gasoline in a diesel car
• If you realize that you filled it with petrol, stop your car at a safe spot and shut off the engine, then tow it to a workshop
• If you realize at the fuel station that you are refueling with the wrong fuel, do not start your car. Tow it to a workshop.
• Gasoline in a diesel car can result in damages to your diesel pump, which can fill up the fuel system with metal chips and damage the whole fuel system. It can result in repair costs of over $10,000.

If you have any questions or want to tell us your story of how you solved this problem, comment down below. If you have any other car questions you are welcome to ask them at our homepage.

Magnus Sellén

Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.