What happens if you put wrong fuel in car? (Diesel & Petrol Misfuelling)

Putting the wrong fuel in your car is something that has happened to more people than you imagine. It is reported that around 150,000 people in the UK alone experience this every year. So, if it counts for something, know that you aren’t alone if this happens to you. In about 3 minutes and 30 seconds, someone else will gasp “Blimey!” for the same reason.

This isn’t exactly your fault. We understand that sometimes the gas pumps might be confusing with their abbreviations and colors, and you may probably be absentminded when refueling.

So please avoid banging your head on your steering wheel because if you are reading this article, you are actually on top of the situation. From understanding your engine to well-detailed remedies for this situation, we are going to tell you how you can fix this problem and avoid unnecessary expenses.

How Do Gasoline Engines Work?

Much of what we are going to tell you in the following paragraphs may not make much sense if you don’t understand how your gasoline engine works. If this is not what you want to read right now, you can skip to the remedies below.

Since we have that sorted out, let’s get right to it, shall we?

Although it was Karl Benz (1844 – 1929) who put together the first gas-powered car, the idea of the “four-stroke” gasoline engine belongs to Nikolaus Otto (1832 – 1891) who invented the engine two decades before Benz attached it to a three-wheeled cart to make the first primitive car.

How it Works

Your typical gasoline engine is built around cylinders (2, 4, 6 or 8 in one engine). They are like mug-sized furnaces where the gas is burnt to produce the energy that moves your car. Unlike mugs, the cylinders in your gasoline engines are made of very strong metals and are sealed tight at their open ends by a piston (much like a bicycle pump).

On top of each cylinder are two valves and a spark plug. The valves are inlet and outlet valves.

Inlet valves are openings that let in air and fuel, and the outlet valves let out burnt gases (exhaust fumes). Both of them can be opened and shut really fast. The fuel comes from a carburetor or an electronic fuel injector.

A spark plug is an electrically controlled device that sparks and creates the fire that burns the mixture of air and fuel in the cylinder that enters through the inlet valve. This step is called intake, and it pushes the piston downwards.

The burning causes the air in the cylinder to expand almost instantly, and that is the force that pushes the piston which is attached to a crankshaft. This combustion (which means burning), expansion and movement of the piston turn the crankshaft which causes the rotation of your wheels. That is the concept of the four-stroke cycle internal combustion engine.

Here is an animation of how it works.

How Do Diesel Engines Work?

A diesel engine is similar to a gasoline engine because their combustion happens internally. What does it mean for an engine to have internal combustion? It means the burning of fuel happens inside the engine.

There are engines in which the combustion happens externally, for example, a steam engine. It has a boiler outside the engine that changes water to steam. The steam is then sent to the cylinder to drive the pistons.

This movement of steam makes the engine less efficient because heat is lost during the flow.

How it Works

The diesel engine is almost like the gasoline engine but with a few differences. One similarity they both share is the 4-stroke cycle.

First, the air enters into the cylinder from the inlet valve and pushes the piston downwards. This engine doesn’t have the spark plug that a gasoline engine has because it isn’t needed.

When the piston moves up and compresses the air in the engine, the diesel is injected at the top of the cylinder, and the burning happens. No need for the spark. And then the expansion caused by the burning pushes the piston that then causes the crankshaft to turn.

Here’s an animation of how the diesel engine works.

How is Diesel Fuel different from Gasoline?

When Rudolf Diesel invented the diesel engine, he ran it on peanut oil. In the past, it was possible to power some diesel engines with many types of hydrocarbon fuels. But today, modern fuel injector systems won’t allow you to run your truck on bad vegetable oil.

The idea was to free people from the dependence on fuels like coal and gasoline. But well, that didn’t turn out exactly how Rudolf wanted.

Gasoline, on the other hand, is a much-refined, higher-grade product of petroleum recycling.

What Happens When You Put the Wrong Gas in your Car?

Putting the wrong fuel in your car, in some situations, can be like stabbing a White Walker with dragon glass. If you don’t get the Game of Thrones reference, it means attacking your car with its poison.

You may be lucky sometimes, and the incorrect fuel won’t flow to other parts of the car, so you have just the tank to deal with. But when it does, what does this mean for your car?

What Happens When You Put Gasoline into a Diesel Engine?

For a diesel engine, the fuel also serves as a lubricant. So putting gasoline in a diesel engine will harm your fuel injector pump.

And that is not all. Do you know that Gasoline ignites faster than diesel? That means in a diesel engine, the gasoline will burn up much quicker than diesel would, and your engine was not designed for that. This will lead to misfires and knocking. Some could be so bad that parts of your engine will get damaged and will either need to be repaired or replaced. That costs a lot of money.

If you are lucky enough to discover the mistake before starting the engine, then congratulations. All you have to do is tow the car and have the tank drained and cleaned.

But if you observe this while driving, you have to stop the engine immediately, have it towed to a mechanic and they will know what to do.

What Happens When You Put Diesel into a Gasoline Engine?

Put Gasoline into a Diesel Engine
Put Gasoline into a Diesel Engine

Did you know that it is better to put diesel in a gasoline tank than to put gasoline in a diesel tank? This doesn’t mean one could work and the other wouldn’t, but in terms of how much damage is done.

Diesel has lubricating properties, so if your diesel engine has gasoline in it instead of diesel, the damage is worse.

Putting diesel into a gasoline engine is less likely to happen because the nozzles used for gas and diesel at stations are different. A diesel pump nozzle will be too big for a gasoline car’s fuel tank. However, accidents could happen.

Since diesel and gasoline have different combustion times, your car will be able to run on the remaining gasoline in the tank. But once it gets to diesel, your engine will shut down on its own.

This doesn’t mean much damage to your vehicle, but you may spend up to $1000 on repairs and tow service. Although you can handle this by yourself by draining the fuel tank, fuel lines, fuel rails, and injector, it is best to consult a professional.

What Happens When You Put E85?

What happens when you put E85
What happens when you put E85

You may have seen some pumps labeled E85. That means the fuel has 85% ethanol and %15 gasoline. If your vehicle is not labeled as a flex-fuel vehicle (or FFV), then this fuel is not for you. The beauty of FFVs is that you can either use gasoline or E85 with no problems.

On the other hand, if you fill your non-FFV with E85, you may have some problems, but it won’t be that serious.

One thing you may notice is that your check engine light is on. If you mistakenly fueled your non-FFV once, you can top it with regular gas and ride it out. The check engine light will eventually go off after riding your car with regular gas for some time.

Octane Ratings

At this point, we need to make sense of what Octane Ratings are before we move on. Octane Ratings refer to fuels and their resistance to knocking during combustion in your car’s engine.

Knocking just means the fuel burned faster than it was intended to, during the compression stroke (remember the 4-stroke cycle?).

This rating is normally used to separate gasoline into three types: Regular, mid-level, and premium. That’s where PMS comes from; Premium Motor Spirit.

These grades of gas each have different octane ratings (or number). The ones with the higher octane numbers are always more expensive.

When You Use the Wrong Octane

What Happens If You Put the Wrong Octane of Gas In Your Car
What Happens If You Put the Wrong Octane of Gas In Your Car

It is easier to make this mistake than that of mixing up diesel and gasoline because the nozzles at the pump for the different grades of gasoline are always the same size.

It could be hard to differentiate them from one another if you are not paying much attention. Also, they are normally found side by side on the same fuel pump.

So what happens to your engine in this situation? Let’s talk about it.

Putting Regular Gas in a Premium Gas Car

If your car requires premium gas, it means it is delicately designed to an extent. Using lower octane fuel in such vehicles can cause long term damage if you continue with it. The problem with this is very hard not to notice.

One major sign of this is the spark knock. You can easily hear a spark knock. It is a high-pitched rattling noise in your engine.

When this happens, your fuel economy will be poorer, and your engine won’t perform quite as well. However, your car engine computers can adjust its timing, but you should switch back to premium gas as soon as possible to avoid permanent damage.

What About Putting Premium Gas in a Car that Doesn’t Need It?

Nothing will happen.

Yes, that’s right, nothing.

There’s a myth that premium gas in a car that doesn’t need it will make the car perform so much better, like using nitro on a race car. This will not happen.

Sorry, but it won’t. The engine computers will adjust the timing to work with higher octane numbers, but other than that, nothing beneficial will happen.

What Should You Do If You Put the Wrong Fuel into Your Car?

Many people can tell stories of that horrible time they put the wrong gas in their car. One common line in that story will be “I didn’t know what to do”.

Here we are to tell you: starting your car and driving away from that embarrassing situation is not the smartest thing to do at that moment. The damage you are doing to your car will come back to haunt you, faster than you think.

Sometimes the problem may not be that bad depending on how much of the wrong fuel is in the tank. If you observed this mistake immediately, and before you got the tank up to 5% filled with the wrong fuel, then check this out: Some mechanics think you can fill up the tank with the right fuel and get away with it.

This is risky though, and you may want to drain the tank to avoid any future problems.

If You Find Out Before Driving…

If you were lucky enough to find out immediately, DON’T START THE ENGINE. You can still save yourself a whole lot of money on repairs if you don’t turn the key.

Only starting the engine can cause the damage to spread from the fuel tank to other parts of the car.

Do these immediately you notice the mistake:

  1. Stop pumping fuel immediately
  2. Don’t start the car or turn the key
  3. Disconnect your car battery
  4. Tow the car or push it away from the pump
  5. Have your car towed to an auto repair shop or garage
  6. Let a professional handle the drainage of the tank and fuel lines

If You Find Out While or After Driving…

  1. Pull over and stop the car immediately
  2. Turn off the engine
  3. Call a tow service to take your car to an auto repair shop or garage
  4. Let a professional handle the drainage, flushing and necessary repairs

How to Fix the Problem of Wrong Gas

There are 3 ways we think you can handle this problem. You could handle it right where you are with a professional, by yourself or take it to a garage. The choice is yours, but we suggest you have the professionals handle this.

  • Roadside Remedy

If you choose the roadside remedy, this is how it will typically go:

You call the companies that specialize in this sort of thing. They arrive at your location. These companies own special vehicles that are equipped with pumps that they attach to your fuel tank. They will use these pumps to suck out the wrong fuel from your tank. Then dissolve the bad fuel with some chemicals. The company people will also have the correct fuel to flush your tank with.

However, you can’t always expect them to be able to change your fuel pump and filters on the spot. On the plus side, it is a relatively cheap solution, but not if you’ve already driven the car with the bad fuel circulating the system.

  • Garage Remedy

In the event, you’ve driven your car with the bad fuel, or even just turned your key to “on”, this could be your only good option.

Call a tow service and have them tow your car to an auto repair shop. Unlike the roadside remedy, this will cost you more money. That is why finding out about the wrong fuel before turning on the engine is the happy side of this horror story.

At the auto repair shop or garage, the mechanics are well equipped to handle your problem and make sure that every sign of this mistake is removed from reality forever.

That is one advantage the garage remedy has over the roadside remedy. The garage remedy can be more thorough.

Sometimes you may think to yourself “this isn’t so bad, I can handle it myself” and opt for having the vehicle towed to your home where you have your DIY tools waiting for you.

  • Do It Yourself

We won’t actually encourage this, but if you want to go ahead, no problem. Here’s how you can go about it:

How to Remove the Incorrect Fuel from Your Tank

Since you believe in your skills and expertise in handling mechanics and working on stuff, we are going to do our best to have your back. There are two ways you can go about this: Gravity draining and siphoning.

  • Gravity Draining

Make sure your car has a drain at the bottom of the fuel tank before doing this.

First, get a jack and raise the car up. Crawl up under it and place a drainage pan under the drainage plug at the bottom of the tank. Unscrew the plug with a spanner and let it flow into the pan.

If the pan is filled up and there is still more bad fuel, tighten it and empty the pan. Then come back under and continue.

  • Siphoning

Please do not insert a hose in your tank and attempt to use your mouth to suck the bad fuel out into a bucket or something. This is how people get high on diesel. Okay, on a serious note, get a siphon kit.

A siphon kit is normally a long hose attached to an air pump. Getting a spark-free model is essential.

Collect the bad fuel in a container and dispose of it properly. The environment thanks you.

If you also change the fuel pumps and fuel filters, either of those two options should work.

However, if you notice any unusual behavior with your car, then you probably didn’t get rid of all the bad fuel, which is rather unfortunate. Then you should take it to the mechanics without feeling embarrassed because you’ve tried.

Can Insurance Companies Help?

Yes, sometimes your insurance company can cover you for misfuelling incidents. Pay attention to the charges though and check the small print to make sure you are actually covered before making a claim. This may not be the case for everyone.

How to Prevent this from Happening Again

Whether this has happened to you before or you can imagine how frustrating this could be and don’t want it to happen to you, there are some things you could to prevent putting the wrong gas in your tank:

  1. Pay attention – We know filling your tank with gas is one of those tasks you can do mindlessly because of how frequently you do it, so you have to pay attention. You should not ignore what your instincts are saying to you. Be awake and read notices and signs on the pump.
  2. Use notes or stickers on your dashboard to remind you – This may sound funny to you, but it could be useful to some people. Subtle reminders on your dashboard could go a long way in reminding you not to make a mistake, especially if you own more than one vehicle and they run on different fuels.

In Summary

Putting the wrong fuel in your car can be very annoying and eat holes into your budget you never expected will pop up. If or when it happens, try to stay on top of the situation. With enough luck on your side, you don’t have to spend so much money on repairs.

Remember that if you notice the mistake early enough, DON’T TURN THE KEY.

Further reading:

  1. Car Engine and How Gasoline Engines Work
  2. How Diesel Engines Work
  3. 150,000 People Put the Wrong Fuel in Their Car Each Year
Avatar for Jack Harris

Jack Harris is a talented and advanced author, blogger, auto expert and senior technical consultant with Autosneed. He is a mechanical engineer who holds a Machine Lubricant Analyst (MLA) Level III certification and a Machine Lubrication Technician (MLT) Level II certification through the International Council for Machinery Lubrication (ICML) and ASE Certified. After years of working as both an automotive journalist and a Ford factory technician, to say I live and breathe the automotive world could still be considered an understatement.

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