Katerina Swanson
Putting unleaded fuel in a diesel car is a common mistake with potentially costly consequences. While older diesel engines may be more forgiving, newer diesel engines are likely to be damaged by the unleaded fuel, which lacks the lubricity of diesel. This can cause issues with the vehicle's fuel pump, injectors, and sensors. If you realise your mistake before starting the engine, you can avoid immediate engine damage by towing the car to a mechanic or dealership for repair.
Can I put unleaded fuel in a diesel car?
| Characteristics | Values |
|---|---|
| Is it possible? | Yes, but it is a common mistake. |
| What to do if it happens? | Do not start the engine. Get the car towed to a mechanic or dealership for repairs. |
| What happens if the engine is started? | The engine may not start or may be undrivable due to loss of power. |
| How much does it cost to fix? | Cost of repairs can be high, ranging from $20,000 to $27,000. |
| How to avoid it? | Diesel and unleaded fuel nozzles are differently sized, and diesel vehicles have a special plate under the gas cap, preventing unleaded nozzles from fitting. |
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What You'll Learn
What to do if you put unleaded fuel in a diesel car
If you've accidentally put unleaded fuel in your diesel car, the first thing you should do is not start the engine. It is important that you do not turn on the engine as this can cause significant damage to the engine and other critical systems.
Older diesel engines are more forgiving and may not be completely ruined by a small amount of unleaded fuel. However, for newer diesel engines, unleaded fuel can cause the engine to die or not start at all. In addition, unleaded fuel can damage the vehicle's fuel pump and injectors as unleaded fuel lacks the lubricity that diesel fuel has. Sensors that record critical engine systems may also be damaged by the unleaded fuel, causing them to overheat or become contaminated with soot.
If you have access to a tow truck, it is best to tow your car to a mechanic or a dealership's service department for a proper assessment and repair. If you are confident in your automotive repair skills and have some DIY experience, you can try evacuating the fuel system by disconnecting the line and commanding the fuel pump to run continuously by jumping its relay. You will need to fully purge the system (including the tank), replace filters, and hope for the best.
If you have a 7.3L or 6.0L Power Stroke, or a 12-valve Cummins engine, you may be able to get yourself out of this situation by immediately draining the tank, flushing clean diesel through the system, and adding new filters.
To summarise, putting unleaded fuel in a diesel car can be a costly mistake that may require professional repair services. It is important to act quickly and avoid starting the engine to minimise potential damage.
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How to prevent putting unleaded fuel in a diesel car
Putting unleaded fuel in a diesel car can cause significant damage to the engine, fuel pump, and injectors. Unleaded fuel can also damage sensors that record critical engine systems, causing them to overheat or become contaminated with soot. Therefore, it is essential to take preventive measures to avoid putting unleaded fuel in a diesel car. Here are some tips to help prevent this costly mistake:
Know Your Vehicle's Fuel Requirements: It is crucial to be aware of the type of fuel your vehicle requires. Familiarize yourself with the owner's manual or seek advice from a trusted mechanic to ensure you are using the correct fuel type for your car. Understanding your vehicle's fuel requirements is the first step toward preventing misfuelling.
Check Fuel Pump Nozzles: Fuel pump nozzles at gas stations are typically colour-coded and labelled to indicate the type of fuel they dispense. Before filling up, take a moment to double-check that you have selected the correct nozzle for your vehicle's fuel type. This simple step can help prevent accidentally putting unleaded fuel in your diesel car.
Be Alert and Focused: Distractions and multitasking while fuelling your vehicle can increase the risk of misfuelling. When you're at the pump, take a moment to ensure you are alert and focused. Avoid distractions such as phone calls, loud music, or engaging in conversations that may divert your attention from the task at hand.
Read Labels and Signs: Pay close attention to the labels and signs on the fuel pump and your vehicle's fuel cap. These labels provide clear indications of the correct fuel type for your car. Take a few seconds to double-check and confirm that you are using the right fuel.
Be Aware of Vehicle Age and Design: In newer vehicles, typically those manufactured within the last 25 years, there is a special plate fitted under the gas cap that prevents the insertion of a diesel nozzle into an unleaded fuel tank. Knowing the age and design of your vehicle can help you understand the built-in safeguards against misfuelling.
Keep a Reminder in Your Vehicle: A simple yet effective way to prevent misfuelling is to place a visible reminder in your car. For example, you can write a note or use a sticker that says "Diesel Only" and place it near the fuel cap or on the dashboard. This reminder can help ensure you always refuel with the correct fuel type.
By following these preventive measures and staying vigilant, you can significantly reduce the risk of putting unleaded fuel in your diesel car, avoiding costly repairs and potential damage to your vehicle.
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Differences between unleaded fuel and diesel
Unleaded fuel and diesel are two different types of fuel with distinct properties and behaviours. The primary difference lies in their chemical composition, with diesel having longer molecular chains and a higher energy density than unleaded fuel. This results in diesel producing more power and being more efficient, especially in trucks and heavy machinery. However, diesel is also associated with increased greenhouse emissions due to its higher sulphur content.
One significant distinction between the two fuels is their behaviour in engines. Unleaded fuel, also known as gasoline or petrol, is designed for use in gasoline engines, which utilise spark plugs to ignite the fuel. In contrast, diesel engines are built to withstand higher pressure and heat, employing compression ignition, where the fuel is ignited by the compression of air rather than a spark. This makes diesel engines more efficient in terms of energy utilisation.
The physical characteristics of unleaded fuel and diesel also differ. Diesel fuel is oily and has a distinct smell compared to unleaded fuel. Additionally, diesel nozzles at fuel stations are differently sized compared to unleaded gasoline nozzles, making it challenging to mistakenly fill an unleaded gasoline tank with diesel. This design consideration further emphasises the importance of using the correct fuel type for a vehicle's engine.
The consequences of mixing unleaded fuel and diesel can be detrimental. Using unleaded fuel in a diesel engine can lead to damage beyond the engine, including the fuel pump, injectors, and sensors. On the other hand, while diesel may work in a gasoline engine, it can cause issues with spark plugs, leading to improper functioning. Therefore, it is essential to ensure that the correct fuel type is used for the respective engine to avoid costly repairs and maintain optimal vehicle performance.
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The cost of repairing damage from unleaded fuel in a diesel car
Unleaded fuel in a diesel car can cause serious damage to the engine and other components. The cost of repairing this damage can vary depending on the extent of the issue and the specific make and model of the car.
If you realise you have put unleaded fuel in your diesel car, it is important not to start the engine. This is because starting the engine can circulate the unleaded fuel throughout the fuel system, increasing the risk of damage. Instead, the car should be towed to a mechanic or dealership for a proper assessment and repair.
Some possible repairs that may be needed include draining and flushing the entire fuel system to remove any traces of unleaded fuel and replacing damaged parts such as fuel injectors, the fuel pump, filters, lines, and seals. The cost of these repairs can range from several hundred to several thousand dollars, and in some cases, the engine may be damaged beyond repair.
For example, one person who put unleaded fuel in their BMW 535d ended up with repair costs of around $27,000, which they had to cover with insurance. In another case, a customer put DEF in their new Powerstroke, resulting in $20,000 worth of repairs.
It is worth noting that older diesel engines are more forgiving, and a small amount of unleaded fuel may not cause significant damage. However, it is always best to consult a qualified mechanic or diesel engine specialist to assess the damage and provide an accurate estimate for repairs.
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The immediate action to take if unleaded fuel is put in a diesel car
Putting unleaded fuel in a diesel car is a mistake that can cause significant damage to the vehicle, including the engine, fuel pump, and injectors. The immediate action to take if unleaded fuel is put in a diesel car is to not start the engine. This is crucial as turning on the engine can cause the unleaded fuel to start doing damage.
If the engine has not been started, the next step is to get the vehicle to a mechanic or a dealership's service department for proper assessment and repair. This may involve towing the vehicle if it cannot be driven without starting the engine. A professional mechanic will be able to assess the extent of the issue and perform any necessary repairs or replacements.
If you are confident in your DIY abilities and are in a pinch, you can try evacuating the fuel system by disconnecting the line and commanding the fuel pump to run continuously by jumping its relay. Fully purge the system (including the tank), and replace filters. However, it is important to note that attempting to fix the issue yourself may void any warranties or insurance coverage related to the vehicle.
It is worth noting that older diesel engines are more forgiving, and a small amount of unleaded fuel may not cause significant issues. In some cases, it may be possible to get away with diluting the unleaded fuel with diesel and taking immediate action to flush and clean the fuel system. However, this is not recommended for newer diesel engines, as they are more sensitive and may not tolerate even small amounts of unleaded fuel.
The cost of repairing the damage caused by unleaded fuel in a diesel car can be significant, and it is always best to seek professional help as soon as possible to minimize the potential for costly repairs or permanent damage.
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Frequently asked questions
Unleaded fuel can cause damage to a diesel car's engine, fuel pump, and injectors. It can also damage sensors that record critical engine systems, causing them to overheat or become contaminated. If you realise your mistake before starting the engine, you can avoid immediate engine damage by towing the car to a mechanic or dealership for repair.
Unleaded fuel lacks the lubricity of diesel fuel, and it also has a lower energy density and faster burn rate, resulting in less efficient combustion and higher emissions.
A small quantity of unleaded fuel (less than 10%) may not cause any noticeable issues. However, as the percentage of unleaded fuel increases, you may experience hard starting and loss of power until the engine won't start or is undriveable.
Do not start the engine. Get the car towed to a mechanic or dealership for proper assessment and repair. If you are familiar with automotive work, you can try evacuating the fuel system, fully purging the system (including the tank), and replacing filters.
Diesel fuel nozzles are a different size compared to standard unleaded gasoline nozzles, and newer diesel vehicles also have a special plate fitted under the gas cap, making the insertion of unleaded fuel impossible. Always pay attention while fuelling your vehicle to ensure you are using the correct type of fuel.
