What Happens if You Put Diesel in a Gas Car

Putting diesel fuel into a gas car is a common mistake that can have significant consequences for your vehicle’s engine and overall performance. Gasoline and diesel fuels have distinct properties and are designed for different types of engines. Mixing them can lead to serious damage and costly repairs. In this article, we’ll explore what happens when you put diesel in a gas car, the effects on the engine, and what steps to take if you’ve made this error.

The Differences Between Gasoline and Diesel Fuel

Gasoline and diesel fuel are both refined from crude oil, but they have several key differences:

Chemical Composition: Gasoline and diesel fuels have different chemical compositions. Gasoline is lighter and more volatile, while diesel fuel is denser and less volatile.

Ignition Process: Gasoline engines rely on spark ignition, where a spark plug ignites the air-fuel mixture. Diesel engines use compression ignition, where the air in the cylinder is compressed until it’s hot enough to ignite the diesel fuel.

Octane and Cetane Ratings: Gasoline is rated by its octane number, which indicates its resistance to knocking or pre-ignition. Diesel fuel is rated by its cetane number, which measures its ignition quality.

Viscosity: Diesel fuel is more viscous, or thicker, compared to gasoline.

Fuel Injection: Gasoline engines use port or direct fuel injection, while diesel engines use direct injection.

What Happens When You Put Diesel in a Gas Car

If you accidentally put diesel fuel into a gasoline car, several problems can arise:

Engine Misfiring: Gasoline engines cannot efficiently burn diesel fuel due to their different ignition processes. The result is engine misfiring, which can lead to poor performance and damage to engine components.

Clogging and Damage: Diesel fuel can clog the gasoline engine’s fuel system, including the fuel injectors and fuel filter. The thicker consistency of diesel can also damage the engine’s components.

Power Loss: Your car’s engine will likely lose power, and you may experience a significant drop in performance.

Stalling: Diesel in a gasoline engine can lead to frequent stalling or difficulty in starting the engine.

Exhaust Emissions: Running diesel fuel in a gasoline car can produce excessive emissions, including unburned fuel, which is harmful to the environment and may result in a failed emissions test.

Catalytic Converter Damage: Diesel fuel can damage the catalytic converter, a critical component in reducing harmful emissions. Replacing a catalytic converter can be expensive.

Check Engine Light: Putting diesel in a gas car can trigger the vehicle’s check engine light, indicating a problem with the engine.

Fuel Pump Damage: Diesel fuel can cause damage to the gasoline engine’s fuel pump due to differences in lubricity and composition.

What to Do If You Put Diesel in a Gas Car

If you realize that you’ve put diesel fuel in a gas car, it’s essential to take immediate action to mitigate the damage:

Do Not Start the Engine: If you haven’t started the engine, do not attempt to do so. Starting the engine will circulate the diesel fuel through the system, increasing the potential for damage.

Tow to a Mechanic: Contact a tow service to have your car transported to a qualified mechanic or repair shop. They can drain the fuel tank and flush the fuel system to remove the diesel fuel.

Do Not Drive: Avoid driving the car with diesel in the tank, as it can cause significant damage and increase repair costs.

Contact Your Insurance: Check with your insurance company to see if the damage from misfueling is covered by your policy.

Repair and Replacement: Depending on the extent of the damage, your mechanic may need to repair or replace components in the fuel system, including the fuel injectors, fuel pump, and filters.

Drain and Flush: The mechanic will drain the diesel fuel from the tank and flush the fuel system to ensure all traces of diesel are removed.

Fuel System Cleaners: In some cases, a fuel system cleaner may be used to help clean out any remaining residue in the system.

Prevention is Key

Preventing misfueling is crucial, as it can save you from the hassle and expense of repairs. Here are some preventive measures to avoid putting diesel in a gas car:

Be Mindful at the Pump: Pay close attention when selecting the fuel type at the gas station. Double-check the fuel grade before starting to pump.

Use a Diesel-Specific Nozzle: If you’re driving a diesel vehicle, ensure you use a diesel-specific nozzle. Diesel pump nozzles are typically larger and have a different shape compared to gasoline nozzles.

Labeling: Some people find it helpful to label their fuel caps with the type of fuel required for their vehicle. This serves as an additional reminder at the pump.

Color Coding: Gasoline is typically green or black, while diesel is often yellow. Pay attention to the color of the fuel handle at the pump to verify you’re using the correct one.

Know Your Vehicle: Familiarize yourself with your vehicle’s fuel requirements and the type of fuel it uses. Make a mental note of your car’s fuel type.


Putting diesel fuel in a gasoline car is a mistake that can lead to significant engine damage and costly repairs. Gasoline and diesel fuels have different properties, and the two are not interchangeable in vehicles. If you make this error, it’s essential to take immediate action by not starting the engine, contacting a tow service, and having the fuel system drained and cleaned by a qualified mechanic. Preventive measures, such as being mindful at the pump and knowing your vehicle’s fuel requirements, can help you avoid misfueling and the associated problems.