Unleaded Fuel In A Diesel Engine: What's The Damage?

Putting unleaded fuel in a diesel car is a mistake that can lead to complex consequences. While older diesel engines are more forgiving, newer diesel engines may die or not start on unleaded fuel. Unleaded fuel in a diesel car can cause engine damage, including to the fuel pump and injectors, as well as sensors that record critical engine systems. The altered exhaust composition from burning unleaded gasoline in a diesel engine also contributes to increased air pollution. If you realise your mistake before starting the engine, it is recommended to get the car towed to a mechanic or dealership for proper assessment and repair.

What happens if you put unleaded fuel in a diesel car?

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The differences between diesel and unleaded gasoline

Putting unleaded fuel in a diesel car can cause significant damage, affecting not only the engine but also the vehicle's fuel pump and injectors. This is because unleaded fuel lacks the lubricity of diesel fuel and acts as a solvent. It can also damage sensors that record critical engine systems, causing them to overheat or become contaminated with soot. While older diesel engines may be more forgiving, newer diesel engines are particularly susceptible to damage from unleaded fuel.

Now, let's delve into the differences between diesel and unleaded gasoline:

Diesel and unleaded gasoline are designed for different types of engines, which function in distinct ways. A diesel engine uses direct fuel injection, delivering fuel directly into the cylinder. It is engineered to withstand high pressure and heat, with the fuel and air mixture being compressed so tightly that it self-ignites. This greater compression makes diesel engines more efficient, allowing them to better utilize the heat generated. Additionally, diesel has a higher energy density than gasoline, containing more energy per litre due to its longer molecular chains.

On the other hand, engines using unleaded gasoline require less pressure and heat. Unleaded gasoline engines use an electric spark to ignite a compressed mixture of petrol and air. Unleaded gasoline has shorter chain molecules and contains less energy per litre compared to diesel.

Another difference lies in their chemical composition. Diesel, with the chemical composition C14H30, contains extra atoms that contribute to increased combustion power. However, these extra atoms also lead to higher greenhouse emissions.

In summary, the key differences between diesel and unleaded gasoline lie in their engine compatibility, ignition methods, energy density, molecular structure, and chemical composition, all of which contribute to the distinct operational characteristics of diesel and unleaded gasoline engines.

The damage to the engine and other systems

Putting unleaded fuel in a diesel car is a common mistake that can have serious consequences. The differences in the chemical composition of unleaded gasoline and diesel fuel mean that the former can cause significant damage to a diesel engine and its various components.

Firstly, unleaded fuel lacks the lubricity of diesel fuel and acts as a solvent. This can cause extensive damage to the engine's fuel pump and injectors, which rely on diesel's lubricating properties. The injectors may be wrecked beyond repair, requiring a costly replacement.

Secondly, the burning of unleaded fuel in a diesel engine produces a different exhaust composition, including increased levels of unburned hydrocarbons, carbon monoxide, and nitrogen oxides. These pollutants not only contribute to air pollution but also reduce the effectiveness of the advanced emission control systems in diesel engines, which are specifically designed for diesel exhaust. The altered exhaust composition can lead to a loss of power and efficiency, as seen in a case where a farm tractor with a diesel engine experienced complications during a busy harvest season due to the use of unleaded gasoline.

Additionally, unleaded fuel can damage sensors that record critical engine systems. The sensors may overheat or become contaminated with soot, leading to improper functioning.

The extent of the damage caused by unleaded fuel in a diesel car depends on various factors, including the amount of unleaded fuel added, the age of the diesel engine, and how quickly the issue is addressed. Newer diesel engines are more susceptible to damage, while older engines may be more forgiving and continue to run even with a small amount of unleaded fuel.

If the mistake is caught early, before the engine is started, towing the vehicle to a mechanic or service center for proper assessment and repair is recommended. This may involve draining the fuel tank, flushing the fuel system, replacing filters, and performing other necessary repairs to mitigate the damage.

What to do if you've put unleaded in a diesel car

Mistakenly putting unleaded fuel in a diesel car is a common error that can lead to costly repairs. If you've put unleaded fuel in a diesel car, the first and most important action you should take is to not start the engine. Starting the engine could cause significant damage, including ruining the vehicle's fuel pump and injectors.

If you realise your mistake immediately, you can try to evacuate 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), replace filters, and hope for the best. Alternatively, you can tow the car to a mechanic or a dealership's service department for a proper assessment and repair.

In some cases, older diesel engines can be more forgiving of small amounts of unleaded fuel. Engines like the 7.3L or 6.0L Power Stroke or a 12-valve Cummins can sometimes get out of this situation by immediately draining the tank, flushing the system with clean diesel, and adding new filters.

It's worth noting that while some people suggest that a blend of diesel and unleaded fuel can be used in extremely cold climates, it is not advisable as it can still cause damage to the engine and fuel system. The use of unleaded fuel in a diesel car can lead to expensive repair bills, and it is always best to seek professional help as soon as possible to minimise potential damage.

The cost of repairs

Misfuelling a vehicle can be an expensive mistake. The cost of repairs will depend on the extent of the damage caused by putting unleaded fuel in a diesel car. If you realise your mistake before turning the ignition on, the issue can be easily and cheaply fixed by draining and flushing out the system. However, if you have driven the car, the repair costs can be high.

Unleaded fuel in a diesel car can cause damage to the engine, fuel pump, and injectors. It can also damage sensors that record critical engine systems by causing them to overheat or contaminating them with soot. The cost of repairing or replacing these parts can vary depending on the car's make and model, the extent of the damage, and the labour costs of the mechanic or dealership carrying out the repairs.

Older diesel engines are more forgiving and may not completely die after ingesting a small amount of unleaded fuel. In some cases, it may be possible to fix the issue by dropping the tank, cleaning it, draining the lines, flushing them out, and replacing the filters. However, newer diesel engines are more likely to die or not start at all when unleaded fuel is added. In these cases, a full engine rebuild may be necessary, which can be costly.

The cost of repairing a diesel car after misfuelling with unleaded fuel can range from a few hundred to several thousand dollars, depending on the factors mentioned above. It is important to note that most standard auto insurance policies do not cover damage resulting from misfuelling. However, some insurance policies may offer optional coverage for misfuelling as part of additional coverage options, so it is worth reviewing your policy or contacting your insurance provider to understand your coverage.

The likelihood of breakdown

The likelihood of a breakdown when putting unleaded fuel in a diesel car depends on a few factors. Firstly, the age of the car is important. Older diesel engines are more forgiving and may not break down immediately after ingesting a small amount of unleaded fuel. Newer diesel engines, on the other hand, are more likely to break down or not start at all when unleaded fuel is used.

Secondly, the amount of unleaded fuel added to the diesel tank makes a difference. If only a small amount of unleaded fuel is added, the car may still be able to run on it without breaking down. However, this is not advisable as it can still cause damage to the engine and fuel system. If a large amount of unleaded fuel is added, the likelihood of a breakdown is much higher, and the potential for damage is also increased.

Additionally, the specific type of diesel engine and the design of the fuel system can impact the likelihood of a breakdown. Some diesel engines may be more susceptible to the negative effects of unleaded fuel, while others may have built-in safeguards or tolerances that can mitigate the issue to some extent.

Furthermore, the immediate actions taken after realising the mistake can also impact the likelihood of a breakdown. If the engine is not started and the tank is drained and flushed before any unleaded fuel is burned, the chances of a breakdown are reduced. However, if the car is driven with unleaded fuel in the tank, the chances of a breakdown during the journey are much higher.

In summary, while there are several factors at play, the likelihood of a breakdown when putting unleaded fuel in a diesel car is generally high, especially for newer diesel engines and when larger amounts of unleaded fuel are involved. Even if a breakdown does not occur immediately, there is still a strong possibility of long-term damage and reduced engine performance. Therefore, it is crucial to take prompt corrective actions, such as draining the tank and seeking professional assistance, to minimise the potential for breakdowns and costly repairs.

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