What Happens if You Put Gasoline in a Diesel Engine?

Diesel and gasoline engines operate differently, requiring specific fuels to run properly. Gas stations use different sized nozzles to prevent mix-ups. However, a smaller gasoline nozzle can still fit into a diesel vehicle’s tank.

While accidentally using the wrong engine oil isn’t ideal, using the wrong fuel can be catastrophic. But what exactly will happen if you accidentally put gasoline in a diesel engine? And what should you do (and not do) if this were to happen?

gasoline in a diesel engine

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

Gasoline vs Diesel

There are a number of key differences between gasoline and diesel fuel, in terms of their composition and functional mechanism. The most obvious difference between these two fuels is the manner in which they are ignited.

Gasoline combusts when ignited via a properly timed spark, from a spark plug. Diesel fuel, on the other hand, combusts under the heat generated by high compression.

The overall volatility of gasoline and diesel fuel is also rated by different overall metrics.

Gasoline is given an overall octane rating, which generally ranges between 87-90+, with the lower end of this spectrum serving as a “standard” grade. On the other hand, diesel fuel is given a cetane rating, which generally falls between 40-55.

Diesel fuel, on average, burns more slowly than gasoline, yet produces higher energy yields with each combustion cycle. Though such figures vary from one application to the next, diesel combustion is generally considered to be 20 percent more efficient by volume than that of gasoline. This produces much of the increased torque, for which diesel engines are known.

Read Also: 7 Different Types of Fuel for Cars

Immediate and Short-Term Effects (of Gas in a Diesel Engine)

There are a number of short-term effects that tend to come as a direct result of adding gasoline to a diesel-powered vehicle’s fuel tank. The most noteworthy of these effects are as follows: 

#1 – No-Start/Stalling

car will not start

In many cases, a diesel vehicle will begin to run poorly shortly after having gasoline added to its fuel tank. This generally results in eventual stalling, followed by a failure to restart, after stalling has occurred.

At this point, fuel system damage and internal engine wear have often already taken place.

#2 – Pre-ignition/Detonation

The addition of gasoline to a diesel engine is also likely to result in a condition known as pre-ignition or detonation. This comes as the result of ill-timed combustion, due to the high temperatures achieved by heightened compression figures standard to the diesel engine.

Pre-ignition is known to result in significant internal engine damage.

#3 – Fuel-System Damage

bad fuel pump

Diesel fuel has natural lubricating qualities that gasoline does not possess. This added lubrication is used to prevent damage to many fuel system components, such as high-pressure fuel pumps. These components can be destroyed in mere minutes without this lubrication.

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

Long-Term Effects (of Gas in a Diesel Engine)

There are also a number of secondary effects that are often attributed to the addition of gasoline to a diesel-powered vehicle’s fuel tank. These effects can take years to manifest, yet are worth keeping in mind, nonetheless.

#1 – Fuel Tank Delamination

Most diesel fuel tanks are lined with special coatings to prevent degradation. When exposed to gasoline, these coatings are known to rapidly deteriorate.

This can mean major issues for the health of your vehicle’s fuel system in the long run. In some cases, it might take 1-2 years for such issues to present themselves.

#2 – Residual Internal Engine Damage

Another definite concern related to the addition of gasoline to a diesel fuel system is the possible internal damage that might have been incurred, yet is not immediately evident.

Though one might not notice any undue or expedited engine wear/degradation at the time of the incident, this does not mean that all damage was avoided. In some cases, this damage is rather minor initially, only increasing in severity with the passing of time.

What to Do If You Accidentally Put Gasoline in a Diesel Engine

There are several things to keep in mind if you ever come to the troubling conclusion that you’ve added gasoline to your diesel fuel tank.

  1. Do Not Start The Vehicle – If you suspect you have accidentally added gasoline to your diesel-powered vehicle’s fuel tank, do not, under any circumstances, start the affected vehicle, or even switch the ignition to the “on” position. Doing so will result in immediate contamination of the fuel system.
  2. Drain The Fuel Tank – Next, drain the affected vehicle’s fuel tank in its entirety. In some cases, this might involve dropping the fuel tank to facilitate draining.
  3. Flush Tank With Diesel – Even after draining the affected vehicle’s fuel tank, it is still a good idea to flush the tank itself with clean diesel fuel. This ensures that no residual gasoline remains.
  4. Fill With Diesel – After all steps above have been completed in their entirety, refill the vehicle’s fuel tank with fresh diesel, and proceed to start-up.

Insurance and Warranty Implications

insurance claim rejected

There are a number of insurance and warranty-related implications that are often associated with the mis-fueling of a diesel vehicle.

In almost every case, the vehicle’s manufacturer will consider any remaining powertrain warranty void, as it stands. Of course, this also means that no coverage will be afforded to assist in the repair of any damage incurred from the mis-fueling itself.

In addition, your individual insurance policy is unlikely to cover any damage caused by the above-mentioned mis-fueling, especially if this policy provides only liability coverage. Even many full-coverage policies stipulate against covering incidences of “neglect”, or lack of attentiveness.

Why Aren’t There Better Systems In Place to Prevent Fueling Mistakes?

what happens when you put gas in a diesel

To date, there is little in the way of safeguards to prevent the mis-fueling of diesel-powered vehicles. This is most likely due to the assumption that human error is unlikely to occur in this regard (which is not always true), and the overall additional costs that would be passed along to fueling stations and/or automakers to develop such safeguards.

At the moment, the most significant safeguard implemented to prevent unfortunate incidents of this nature involves the usage of different diameter fueling nozzles for gasoline and diesel applications.

In most cases, a diesel fuel nozzle will not fit in a gasoline fuel tank filler neck. On the other hand, a gasoline fuel nozzle will fit in a diesel fuel tank filler neck, but it will be extremely loose and ill-fitting.

Josh Boyd

11 Comments

  1. I heard that farmers would put a gallon of gas to a tank of diesel in the winter and cold temperatures so that it would start easier. Anyone else heard of this?

  2. I added 2 gallons of gasoline to my 1981 diesel burning 555B Ford Backhoe. I didn’t start it up until I siphoned all the fuel out. It ran for about 2 minutes and then shut off and wouldn’t start back. Does the fuel pump have to come off to be filtered?

    1. I don’t know for sure, but my gut tells me you will want to make sure all gasoline is out of the fuel system before you run the engine again.

  3. What should i do the gasoline boy puts 1.8litters of gas in may diesel engine then they tell me its ok because its not that huge amount of gasoline is it ok?

    1. No, that’s not good for the engine. Have you driven the vehicle since the gasoline was added? You may want to consider towing the vehicle to a place that can drain the gasoline out of the tank.

  4. Get every once of gas from the fuel system, lines, everything, replace the fuel filter and add diesel, cross fingers. Pumping out sounds good but…you will not get every bit of the gas out, and mixing the two will cause more problems, engine damage.

    1. Way back when before all these fancy additives where around they would mix gas into diesel so that it wouldn’t gel up when it was cold out. New stuff I wouldn’t do that 2 but older diesel engines I would top it off with the proper fuel and run it.

  5. I recently went to fred meyer here where i live in oregon and the gas attendant put a few gallons of gasoline in my diesel 2003 passat which was almost empty not knowing he did this i left the store heading home and only made it about a mile before my car started struggling and died. Not aware yet of the issue i pumped the gas pedal and started my car again and drove toward a parking lot. I didnt make it far before my vehicle died again. Thats when it accured to me i had the wrong fuel. I need to know what should be replaced considering not only did i drive until it died but after started it and drove again until it died if someone could please give me a little guidance i should greatly appreciate it.

    1. Ugh, this is why every state should have self-serve gas. I personally hate driving in Oregon because of this. My understanding is, once you left the gas station, they are no longer liable.

      I wouldn’t drive it again without pumping out all the fuel in the tank. Then add a few gallons of diesel and see what happens. I think you will be fine though. You aren’t the first person this has happened to (nor will you be the last).

    2. Hi, i accidentally did this to my triton 2017. Similar things happened to the both us. The gasoline boy puts unleaded to my diesel. I’d truly appreciate it if you tell me what happened to your car after the incident.

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