What Happens If You Put Diesel In Gas Engine?

Diesel and gasoline engines are both internal combustion engines that run on different principles and use different fuel types.

Gasoline engines ignite compressed air-fuel mixture through the spark plugs to create combustion. This forces the pistons to move up and down and keep the engine running. 

Diesel engines, on the other hand, work with compression instead of using spark plugs. It compresses only air in cylinders and injects diesel fuel into the hot, highly compressed air, and the heat generated in the highly compressed air ignites the fuel, creating combustion that keeps the engine running.

Diesel and gasoline are two different fuel types, and an engine that runs with one is incompatible with the other. But what happens if you put diesel in gas engine?

how long does it take for diesel to ruin a gas engine

The effects of putting diesel in a gas engine

Putting diesel in a gas engine is bad enough. Trying to drive the car will cause the engine to stall and jerk as soon as the fuel reaches the injectors, which will cause many things, such as clogging the fuel lines and other engine components. The good news, putting diesel fuel in your gas engine won’t damage it, though it may require replacing some parts.

The severity of the problem will depend on how much gasoline you had already in the gas tank and the quantity of the diesel you poured in. For example, adding 1 to 5 gallons of diesel in a nearly-filled gasoline tank will be minor compared to filling an empty gas tank with diesel.

While putting diesel in gas could result in several issues, depending on your situation and car model, cars with a little diesel in gas engine will still run and drive, but you will experience hard starting, reduced power, reduced fuel efficiency, and excess exhaust smoke.

But if you pour a larger amount of diesel into a gas tank, the fuel pump will struggle to move the diesel/gasoline mixture into the engine, which could prevent the car from starting.

Also, diesel fuel will not easily cross the gasoline fuel filter. Instead, it can clog it, and any diesel that finds its way across the filter may clog the fuel injectors, making them malfunction or inoperable.

how to fix diesel in gas engine

Signs of diesel contamination 

Before discussing how to fix diesel in a gas engine, let’s see how to find out if you have diesel in your gas engine.

Sometimes, the driver knows what happened. It could be he was carried away with something and didn’t know when he grabbed the diesel nozzle, only to find out after filling the tank with diesel fuel.

Most times, we receive a call in our garage that a car stalls and refuses to start after a while, or the vehicle is towed down to our garage.

If you don’t know, you don’t know. One of the most common diesel in gas engine symptoms is car stalling or dying right after visiting a gas station.

If you suspect you have diesel in a gas engine, sniff the exhaust tailpipe; it’ll smell a bit like diesel. If you are not convinced about that, loosen the spark plugs; it’ll be oily and wet and have a strong diesel odor.

How long does it take for diesel to ruin a gas engine?

Your gas engine will stall or jerk once the diesel reaches the engine, and it will shut off shortly after. Other than preventing the car from starting when the diesel is still in the tank, it won’t damage your engine.

The highest it can do is to foul the spark plugs, clog the fuel filter, and weaken the fuel pump. Believe it or not, it won’t ruin your engine. Disregard any information saying otherwise.

The steps to fix the problem

What should I do if I accidentally put a little diesel in my car? While putting diesel in gasoline is bad, the good news is that it won’t damage your engine. Here’s a simplified guide on how to fix diesel in gas engine.

To fix the problem, drain all the fuel in the gas tank. You want to make sure you empty it. Then, pour fresh gasoline into the tank. Add enough gasoline to the tank because some diesel will be left in the car, and you have to dilute it properly. After that, pull out the spark plugs and clean them.

Keep in mind that if you add too much diesel to the engine, it may damage the fuel pump and filter, and you will have to replace them. It is a simple fix that you can do at home. The hardest part is completely draining the diesel fuel from the gas tank.

The costs of repairing the damage

The diesel in gas engine repair cost depends on your location, the mechanic doing the job, and whether your car has a fuel tank drain plug. If the car has a removable fuel tank drain plug, it will make the work easy. The mechanic will just have to remove the drain plug to drain all the fuel in the tank. He will then fill the gasoline in the tank and drain it again to remove all the diesel in the car.

But if the car doesn’t have a fuel tank drain plug, the mechanic will have to drop the tank and the floor to remove the diesel/gasoline mixture. The mechanic will have to rinse the tank a couple of times to remove all the diesel in it.

Draining fuel in the gas tank could cost around $150 to $450, depending on whether you have a removable fuel drain plug. But if the diesel fuel has entered the engine, you will have to pay up to $700 to fix it. Again, this depends on your car model.

can you put gas in a diesel engine

The prevention tips

Adding diesel fuel to gas engines is not common, though it happens. To avoid making this mistake, pay attention when refilling your fuel tank. Look at the fuel nozzle properly. Here’s how to tell diesel from unleaded gas.

The fuel nozzle on diesel pumps are larger than the ones on gasoline pumps

The diesel fuel nozzles are usually colored green

Diesel fuel smells like kerosine, while gasoline smells like paint thinner.

If you keep these things in mind every time you get to a self-serve gas station, you avoid making this mistake. However, if you live in a region where gas stations have gas attendants, always confirm you are buying the right fuel.

Final words

Adding diesel to a gas engine is bad enough. Do not add to it by driving it. If you notice you have added diesel into your gas tank, do not start the engine. Have the vehicle towed and the diesel drained out.

You have seen what happens if you put diesel in gas engine. Hence, you should prevent it from happening in the first place. The best way of doing this is by paying close attention when next you get to a filling station.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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