What happens when you mix gas and diesel

Gasoline and diesel both made from crude oil and come out of pumps at the gas station — but that’s about it in terms of similarity. Gasoline and diesel engines are built differently, and they’re only going to work with the appropriate engine. Mixing the two fuels, or putting the wrong kind of fuel in your tank, can be a costly mistake.

The Difference between Diesel and Gasoline

Both diesel and gasoline are fuels derived from crude oil. Diesel is both more stable and more energy-dense than gasoline (which is why diesel has such great fuel economy). As a result, diesel needs more compression than gasoline to ignite. Most often, diesel engines are compression engines, and gasoline engines are spark-ignition engines. Beyond that difference, both kinds of engines work on about the same principles, despite the chemical differences between diesel and gasoline.

What Gasoline Does to a Diesel Engine

The short answer is nothing good.

The long answer is the gasoline will either not combust, or, because gasoline is different in composition compared to diesel (with gasoline being generally more volatile and explosive), the gasoline will combust at the wrong stages in the diesel engine’s combustion process. While a diesel engine is built to withstand the force of combustion, combustion at the wrong time can lead to serious damage to almost every component of the engine — especially the pistons and connecting rods.

Diesel is also a lubricant, while gasoline is not. If gasoline makes its way into a diesel engine, it can jam the fuel pumps and the injectors. So gasoline will gum up the works in a few different ways, all of which can be expensive to repair.

Diesel engines will run on a lot of different types of fuel (including biodiesel and leftover frying oil), but they will not run on gasoline. Mixing in a little amount of gasoline with diesel is a bad idea, but might not be catastrophic. A large amount of gasoline will cause significant damage to a diesel engine.

The good news is it that it is relatively difficult to mis-fuel a modern diesel engine. Starting around 2009, manufacturers began adding mis-fuel protection devices to diesel vehicles. Vehicles with these protection devices will only accept diesel fuel (or fuel from diesel pumps). If a diesel is older than that, however, it’s probably still at risk for mis-fueling.

If you’re wondering what diesel does to a gasoline engine, the answer is a lot less. Gas engines can’t combust diesel fuel — there’s not enough pressure in the engine. If you pump diesel into a gas engine, you’ll drive until you run out of gasoline and then stop. The diesel will then need to be flushed out of the fuel tank, and the engine itself before the engine will run again, however. The process of getting all of the diesel out can be difficult. Sometimes, the engine will need to be completely taken apart, cleaned and then put back together.

What to do if you Fuel a Diesel Engine with Gasoline (or Vice Versa)

First of all, don’t start the engine. You might be tempted to be polite and move your vehicle out of the way of the pump. Starting the engine, however, puts it at risk of damage right away. Instead, let the gas station attendant know you won’t be able to move the vehicle right away and pay for the fuel that you’ve dispensed.

Call your roadside service provider or a towing company and have your car brought to a dealership or mechanic. Once there, let them know what’s happened, and they’ll flush your fuel tank. This can be a little expensive — anywhere from $50 to $100 — but it absolutely beats damaging the engine, or having to pay to have your entire engine flushed of fuel.

Mixing Gasoline and Diesel Fuel

Mixing gasoline with diesel (or vice versa) will at best cost you a good chunk of money. Stick with the fuel for your engine, and if you do accidentally fuel up with wrong kind, don’t try to drive on it — it won’t end well.

Scott Huntington is an automotive writer from central Pennsylvania. Check out his work at Off The Throttle or follow him on Twitter @SMHuntington.

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.

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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)

Table of Contents

• Top 6 Effects of Gasoline in a Diesel Engine
  • #1 – No Ignition
  • #2 – No Lubrication
  • #3 – Fuel System Damage
  • #4 – Shock Wave Damage
  • #5 – Engine Damage
  • #6 – Black Smoke
• What to Do and Don’t Do

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.

What would happen if you mixed gas with diesel?