What Happens if You Put Gasoline in a Diesel Engine?

If you’re at the gas station and you accidentally fill your diesel engine vehicle with regular gasoline, then it can cause a lot of problems for your vehicle. You see, diesel engines do not depend on spark plugs like gasoline engines do.

The gasoline engine depends on the spark plug for the gasoline fuel to ignite in the combustion chamber. The diesel engine, on the other hand, uses high amounts of air compression while diesel fuel gets injected at the right time afterward.

That is the difference between the two engines and so mixing fuel with the wrong engine will only cause problems.

Most gas stations use different nozzles to pump gasoline or diesel into a vehicle’s gas tank. A diesel nozzle has a larger diameter than a gas nozzle. Most modern gasoline engine vehicles (manufactured after 1990) simply won’t allow a diesel nozzle to physically fit in the gas tank’s filler neck.

But since a gasoline nozzle is smaller, it can fit into the filler neck of a diesel engine vehicle making it easy to put in the wrong fuel in a diesel car or truck.

While accidentally putting the wrong engine oil in your vehicle is usually a minor issue, putting the wrong fuel in your vehicle can be catastrophic.

Related: Bleach in a Gas Tank? (What Really Happens)

Top 6 Effects of Gasoline in a Diesel Engine

If you catch this problem early enough, you may be able to prevent serious damage from being done to your vehicle. But if you keep driving your vehicle with the wrong fuel in it, then you might experience all these problems.

Here are six issues you may experience if you put unleaded gas in a diesel engine:

Read Also: 7 Different Types of Fuel for Cars

#1 – No Ignition

A diesel engine is not designed to ignite fuel. Gasoline is designed so that it won’t ignite automatically (it requires a spark plug to ignite). Therefore, when gasoline flows into a diesel engine, there will be no ignition that takes place.

If by chance there is an ignition since diesel is mixed with gas, it will be too severe for what the engine can handle.

#2 – No Lubrication

A lot of people forget that diesel fuel is basically the same as oil as it lubricates a diesel engine’s components. If you put gasoline (a solvent) into the engine, it’s not made to lubricate these parts.

Instead, it will contaminate them while they receive no lubrication. As a result, the metal components will rub against each other and became permanently damaged.

See Also: Water in a Gas Tank (What Happens)

#3 – Fuel System Damage

Gasoline will certainly affect the fuel injectors, fuel pump, and fuel filter of your diesel engine. This makes up the whole fuel system of your vehicle.

Without these components working properly, you will have to replace your fuel system entirely.

Read Also: Fuel Gauge Malfunction (Causes and Repair Cost)

#4 – Shock Wave Damage

There are lots of reciprocating parts and components inside a diesel engine, such as rods, pistons, and wrist pins. If there is an unusual detonation that is uncontrollable, the shock waves from the detonation could damage or destroy these components.

Gasoline can surely cause a detonation that the diesel engine’s components cannot handle.

#5 – Engine Damage

If the problem is caught soon enough, the engine can be salvaged before it is too damaged beyond repair. But the longer you attempt to drive with the gasoline in the diesel engine, the more likely your engine will be completely destroyed. And as you probably know, replacing an entire engine is very expensive.

#6 – Black Smoke

Octane rating is a fuel’s resistance to combustion under pressure. Gasoline has an octane rating between 87 and 93 AKI. Diesel is closer to 25. Since diesel has a much lower octane rating than gasoline, gasoline will have a much harder time igniting in a diesel engine, which means a lot of unburned fuel.

This will show up as large amounts of black smoke coming out of your exhaust. While the smoke itself looks and smells bad, it also signifies that various parts and sensors in your fuel system will eventually clog up because of soot.

What to Do and Don’t Do

If you realize that you put the wrong fuel in your diesel engine at the gas pump, don’t panic (well ok, maybe a little). There are a few things that you can do to save your vehicle from sustaining any real damage. Below are the top five tips that you should follow in a situation like this.

1. 1. DO NOT try to start the engine. Leave the vehicle exactly where it is.
   2. DO NOT try to turn on the ignition. Any attempt to turn the ignition key to the “On” position will cause the fuel pump and fuel injectors to activate.
   3. If you already managed to start the car and started driving before you realized your error, pull over to the side of the road or a parking lot and call for a tow truck.
   4. Call for a tow truck to come and tow your vehicle away from the gas station. Have them take your vehicle to your local dealership or any trustworthy auto mechanic.
   5. The fuel tank will need to be completely drained and the fuel system flushed out. As long as the vehicle was not turned on, the gasoline will not have contaminated any of the internal components.

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Mark Stevens

Owner at Car Treatments

Mark is a veteran auto technician who has honed his skills with over 19 years of service at Ford and Mazda as well as some independent work. He's known for his attention to detail and problem-solving skills and enjoys coming up with out-of-the box solutions when the situation requires it.

When he's not troubleshooting customers' cars, you'll most likely find him working on his current project ('96 Bronco) or cooking Italian food for his family.

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