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The Hidden Dangers of Diesel in Gas Engines

What to Do If You Put Diesel In a Gas Engine

First and foremost, don’t panic. If you have accidentally put diesel fuel in your gas engine, the situation, although inconvenient, is manageable. The key is to not start the vehicle. Starting the engine with diesel in the gas tank can cause costly repairs as the diesel may seize the engine or clog the fuel line, leading to extensive repairs.

Next, approximate how much diesel was pumped into the tank. If it’s a small drop in a mostly full tank of gasoline fuel, the issue might not be as severe. However, if a significant amount, say 50% or more, of the tank is filled with diesel, immediate action is necessary. Leaving diesel to sit in a gas tank can cause further damage.

Your best course of action is to call a local garage you trust and explain the situation. They will likely recommend draining the tank. Meanwhile, arrange for a tow truck to transport your car to the garage. It’s crucial to have the car towed rather than driving it yourself to avoid the risk of the diesel fuel entering the engine system.

By acting swiftly and sensibly, you can minimize the damage and ensure your car gets the proper care it needs.

What Happens If You Put Diesel in a Gas Engine?

When diesel fuel, with its octane rating of 25-30, is mistakenly put into a gasoline engine, which normally requires a fuel grade with an octane rating of 87-91, it leads to numerous problems. According to the U.S. Department of Energy, the octane rating is a measure of a fuel’s ability to resist knocking or pinging during combustion. Diesel in a gasoline engine disrupts the air/fuel mixture, causing it to detonate prematurely and inefficiently. This damage can significantly impact the engine’s ability to ignite and run efficiently, resulting in diesel contamination. The consequence is not just limited to reduced efficiency but extends to significant damage to interconnected parts of the car, necessitating costly repairs and sometimes even complete replacement of components.

What is the Difference Between Gasoline Fuel and Diesel Fuel?

Diesel fuel and Gasoline Fuel are both derived from crude oil, but their applications and properties are markedly different. Diesel fuel, used primarily in diesel engines found in eighteen wheelers, trains, buses, and boats, is a distillate fuel. Its larger molecules make it heavier and thicker in consistency, resembling a lightweight oil. This density and viscosity difference means it has a lower autoignition temperature than gasoline. Diesel engines are designed to utilize this feature, operating without spark plugs and relying on compression to ignite the fuel. On the other hand, Gasoline Fuel, with its lighter and thinner properties, possesses a distinct odor and is often mixed with ethanol – a flammable organic compound. This makes gasoline more suitable for gasoline powertrains in passenger cars, SUVs, and light-duty trucks.


While diesel engines are known for their high torque rating and low-end pulling power, making them ideal for heavy-duty trucks and semis, gasoline engines, equipped with spark plugs, use a spark to ignite the fuel. This fundamental difference in combustion methods underscores the specific fuel-type requirement for each engine. Gasoline engines, with their higher autoignition temperature, use the spark plugs’ pressure to create a lit with fire ignition, whereas diesel is squeezed and heated up by the engine’s pressure.

What is the Difference Between Gasoline Fuel and Diesel Fuel

Therefore, while both types of fuel originate from the same source, their physical properties, combustion techniques, and engine designs are distinct, each catering to specific vehicle types and performance needs. Using the wrong type of fuel in an engine can lead to significant damage to the fuel system and engine components, given their tailored design for a specific type of fuel.

What Happens if You Put Diesel in a Gasoline Car?

Accidentally filling a gasoline-powered vehicle with diesel fuel is a common mistake often made at fuel pumps where the gas nozzle and diesel nozzle are situated close together. Despite diesel nozzles being labeled in vibrant green to differentiate them and designed too large to fit into a vehicle’s gasoline filler neck, drivers not paying attention may still grab the wrong nozzle and pump the wrong kind of fuel into their tank. This leads to diesel contamination in the gasoline car’s fuel system, posing severe consequences for the engine’s health and operation.

If diesel fuel enters a gas car, it can disrupt the engine and fuel system, potentially necessitating replacing parts. The problems faced depend on the amount of diesel in the tank. A small proportion of diesel in a mostly full tank of gasoline may allow the car to still run and drive, albeit with symptoms like difficulty starting, reduced power, emitting smoke from the exhaust, and catalytic converters failing due to excess unburnt fuel and particulates. However, a larger proportion of diesel in the tank, especially in an empty tank, means the car won’t start at all, due to different combustion properties of diesel compared to gasoline.


What Happens When You Put Diesel in a Gas Vehicle?

Putting diesel fuel in a gas vehicle causes significant issues due to diesel’s thicker and denser nature compared to gasoline. The fuel pump struggles to move this mixture through the system, and the diesel fuel often fails to pass through the fuel filter, leading to a clog. This can render the fuel injectors inoperable, resulting in the engine gumming up and seizing. The vehicle might run for a short period on the remaining gasoline in the fuel line, but soon, the early ignition and volatility of the diesel-gasoline mix, which has high combustion tendencies, could lead to catastrophic damage to the engine and its components. This mistake is particularly dangerous if diesel fuel is poured into a diesel tank designed for gasoline, as diesel’s properties do not allow it to ignite as sooner as gasoline, leading to severe operational failures.

What Should You Do if You Put Diesel in Your Car?

If you accidentally put diesel fuel in your gas tank, it’s crucial to take immediate action, as leaving diesel in a gas tank is not advisable. First, don’t start your vehicle; starting could push diesel into the fuel line and engine system, complicating the repair process and making it more costly. The best step is to have your car towed to a garage for drainage. If your vehicle has a removable drain, the mechanic can open it to empty the gasoline/diesel mixture and then fill and drain the tank again to remove all remaining diesel. This process may need repetition to clear the tank of diesel contamination thoroughly. If there’s no removable drain, the tank will have to be dropped and rinsed with fresh gasoline until all diesel is washed out. Draining the tank can cost between $200-$500, depending on the needs and present state of the vehicle. If diesel has entered the fuel line or engine, the repair job can escalate to the $1,500-$2,000 range.



The cost to fix a gasoline car that has been filled with diesel fuel can vary widely, depending on several factors. These include mechanic labor rates, the type of car you own (with luxury cars typically being more expensive to repair), and the severity of the problem. In simpler cases, where immediate action is taken, you might only need to pay a few hundred dollars for the tow to a local mechanic and the fee for draining the tank and flushing the fuel system. However, if critical parts like the fuel injectors, fuel pump, or catalytic converters need to be replaced, the costs can escalate into the thousands.


To avoid the time-consuming and potentially expensive problem of putting the wrong type of fuel in your vehicle, it’s crucial to be vigilant at the gas station. Gas stations often take precautions to prevent such mishaps; for instance, the filler nozzle for diesel is typically made too large to fit into a gasoline car’s fuel filler. Also, many stations color the diesel pump handle green as a visual cue. Despite these measures, there’s still a chance of accidentally using a fuel can filled with diesel by mistake and then pouring it into your car. The best way to avoid this is to always pay attention to the type of fuel you’re selecting, especially if you’re in a hurry or distracted.

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