• Diesel
• Gasoline
• Misfuelling
• Wrong fuel
• What happens
• What to do
• Mechanic
• Garage
• Vehicle
• Car

Accidentally placing gas in a diesel car (or the other way around), is not as rare as you might think.

A moment’s distraction, zoning out due to tiredness and stress, or even plain forgetfulness could place anyone in an even worse situation – which will not only disrupt whatever plans you have for that day, but also your budget.

And, honestly,  we are not here to judge.

One common misconception is your car won’t work ever again when it happens. 

The good thing is that’s not always the case. 

Learn what to do to prevent adding more injury to yourself and your vehicle.

But before that, let us help you understand what the differences are between gasoline and diesel, and what happens when diesel and gas fuel mix; so you’re not left in the dark when it happens to you.

What is the difference between gasoline fuel and diesel fuel?

Diesel fuel

Diesel fuel is a type of distillate fuel produced from crude oil.

Its molecules have higher density than gasoline; thus, also having higher viscosity.  

It is also worth noting that a diesel engine is created for self-combustion, which means that it doesn’t need a spark plug. 

Diesel fuel is compressed and pressurized until it becomes so heated that it ignites all by itself. 

Most diesel nozzles usually don’t fit into new gas tanks, and they smell differently compared to gasoline.

If you are a long-time car owner, you should be able to distinguish one from the other by just how they smell.

Gasoline Fuel

Like diesel, gasoline fuel came from crude oil, but with a different chemical make up. 

Gasoline is usually mixed with around 10% ethanol, but it still has a higher auto-ignition temperature than diesel. 

Unlike diesel, gas engines require a spark plug to combust. 

What happens when you put gas in a diesel car, or vice versa?

Pumping diesel into a gas tank

It will cause a  molecular imbalance.

As mentioned above, diesel is thicker than gasoline because it is made up of larger, heavier molecules. 

Since diesel fuel has an octane rating of 25-30, while gasoline fuel usually has an octane rating of 87-91, pumping diesel fuel into a gas tank can lower the octane level needed to reach its flash point and auto-ignition temperature.

Imagine how much combustion would take place for a gas engine motor vehicle that uses a spark plug to prematurely ignite a diesel-contaminated fuel. 

All of this can cause significant damage to the engine and the other connected parts that work together to run your vehicle.

Clogged fuel pump and diesel injectors

Since diesel fuel is thicker and denser than gasoline, the fuel pump will struggle to move the diesel-gasoline mixture through the system. 

Moreover, the fuel filter of a gas engine is specifically designed for gasoline fuel. Hence,  a much more viscous diesel fuel will not easily pass through, resulting in your engine gumming up and seizing, until it’s no longer operable.

Cylinder and timing problems

It can also cause cylinder and timing problems because while a gas engine motor vehicle uses a spark plug to ignite the fuel, the engine cannot maintain enough heat and compression to combust the diesel correctly. 

Yes, your car will continue to work for a little while, but only until all the gas fuel is consumed. Once you are left with diesel fuel, your vehicle will  eventually slow down and stop running completely. 

Pumping gas into a diesel tank

As bad as pumping diesel fuel into a gas tank may be, the reverse scenario – pouring gasoline into a diesel tank – would be far worse. 

Damaged sensors and  fuel pump

Running gasoline in a diesel engine will cause your computer sensors to malfunction as it tries to compensate for the gasoline’s lack of lubricity, not to mention, its corrosive qualities. 

A fuel pump running without lubrication will soon result in its metallic components grinding against each other. Its surfaces will then begin to disintegrate, and those microscopic particles can do even more damage to your car's engine.

Since diesel engines have a higher combustion capability, the gasoline-diesel mix will produce a black smoke coming out of your exhaust.

What to do when you put petrol in a diesel car and vice versa?

Pumping diesel into a gas tank

Approximate how much of the wrong fuel was pumped?

It would be really helpful to know how much you pumped into your tank. Was it a drop or more than half? It would be great to let  your mechanic know. 

Do not operate the vehicle. 

Don’t switch on your engine and avoid placing your keys in your car’s ignition. For modern cars, unlocking it might also not be a good idea. Some newer versions of vehicles can immediately activate the fuel pump once you unlock it. 

Minimize the risk of costly repairs by not running the vehicle. Your engine could seize and consequently lead to more expensive repairs if it continues on sucking up the contaminated fuel. 

Although several forums say that gasoline won’t immediately lead to your vehicle falling apart, the long-term damage may be beyond saving. The cost may not be worth the risk. 

Call a tow truck now.

Reach out to a tow truck company to deliver your car to your local garage. It is advisable that the bad fuel is drained as soon as possible.  

Although you can drain your fuel on your own, do not attempt unless you are 100% confident in doing so. It is highly important for a  reliable mechanic to ensure every drop of the bad fuel is properly drained out. 

Contact a garage immediately.

Reach out to your trusted mechanic. Most of the time, they would recommend draining your tank. Make arrangements with the garage so the tow truck can deliver your car directly to them.

Have your mechanic drain all the bad fuel.

If there is no removable drain on the tank, your mobile mechanic will have to remove the tank from the vehicle. This is called “dropping the tank.” They will then have to rinse the tank repeatedly with fresh fuel to ensure that all of the contaminations are washed out. 

If contaminated fuel has entered the fuel line or engine, expect a more costly repair.

It is also important to let your mechanic know if you have started before it was inspected. In this case, they will have to inspect your engine, diesel injectors, and fuel pump to determine any damage caused by premature ignition, lack of lubricity and the like.

Forgetfulness Tip: 

Put a label on the gas cap. You wouldn’t want this to happen to you, and would never want it to happen again, if it already did. 

It may sound silly, but if doing so will prevent you from spending on expensive repairs, as well as taking a lot of your precious time, then this simple note should be worth it.  

Final Word

Most (if not all) car warranties and insurance do not cover misfuelling, so it is important to ask them before signing a deal. 

If you are lucky to have that included in your insurance coverage or warranty, the last thing you want is to cover  all the expenses for something that could be shouldered (whether partly or full) by your insurance company.