What Happens if You Put Diesel in a Gas Car?


Accidentally putting diesel in a gas powered vehicle is an easier mistake to make than you might think. While diesel pumps are clearly labeled, they’re usually right next to the gas pumps. If a driver isn’t paying attention it’s not difficult to grab the wrong pump. So, what happens if you make this mistake, and what should you do?

Putting diesel in a gasoline powered car is not good for the car, and can cause extensive damage if you continue to operate the vehicle. If you accidentally put diesel in your gas powered car, you should have your vehicle towed right away so it can be drained.

This article will go into the differences between diesel and gasoline, as well as giving more detail on what to do if you put diesel fuel in your gasoline powered car by mistake and what damage it can cause to your car.

Related: What Color is Gasoline?

What is the Difference Between Diesel and Gasoline?

You may be surprised, but gasoline and diesel engines have many similarities.

  • Both engines are internal combustion engines that transform the chemical energy in fuel to mechanical energy.
  • Both have pistons that move up and down within cylinders, with fuel combustion driving the movement in both cases.
  • These pistons are connected to a crankshaft, which rotates as the pistons move to generate the vehicle’s propulsion energy.

The distinction between the two engines lies in the method of gasoline ignition. In the cylinder of a gasoline engine, fuel and air are combined. The mixture is compressed by the piston and ignited by a spark from the spark plug. In diesel engines, spark plugs are absent. Instead, the air and fuel are ignited by the compression itself, which causes a small explosion that moves the pistons.

Image Courtesy of Car Throttle

Because of these differences, gasoline is much more flammable than diesel. So while it’s not good to put diesel in a gas powered car, it’s much worse to accidentally put gasoline in a diesel powered vehicle.

Luckily, the nozzles of diesel and gasoline pumps are different sizes, and the nozzle of diesel pumps is difficult to fit into a gasoline tank. Therefore, the chance of most people making this mistake and not noticing immediately is slim.

How Can Diesel Damage a Gasoline Powered Car?

If the vehicle hasn’t been started, there shouldn’t be irreparable harm. All that will be necessary is to empty the diesel. However, if you do start the vehicle, the fuel pump will attempt to flow diesel through the engine system.

As diesel is far more viscous than gasoline, it will clog any engine parts it reaches, beginning with the fuel filter, and ending in the catalytic converter. The vehicle may also be severely smoky and loose power, and while it may continue to operate while the remaining fuel is burned up, the engine will ultimately fail if you continue driving.

The magnitude of the damage will also depend on the amount of fuel used. If there are only a few drips, the effect may be minimal. However, the more fuel you put in before noticing your error, the greater the damage your vehicle will experience if you attempt to start it.

Effects of Putting Diesel In Gas Powered Car

  1. Harder To Start: Diesel will make the fuel thicker, and the “thicker” fuel probably won’t evaporate enough to mix evenly with the air. Basically, the contaminated fuel will either stay concentrated in a single jet or break up into droplets that are too big to burn evenly, if it even starts to burn at all.
  2. Smoke Heavily: Despite the fact that engines cannot generate sufficient compression pressure to ignite diesel, some of it may still ignite due to the presence of combustable gasoline the gas tank. In this case, neither the gasoline nor the diesel in the fuel will completely combust, resulting in the production of dense clouds of smoke.
  3. Loss Of Power: Limiting the combustibility of gasoline by contaminating it with diesel will result in poor combustion and a loss of power. If the engine can still run at all, you are almost certain to have serious misfires, bad idling, and much higher fuel use.
  4. Clogged Catalytic Converter: Catalytic converters are only designed to withstand limited amounts of unburned hydrocarbons. Consequently, gasoline containing even small amounts of diesel might increase the amount of unburned hydrocarbons in the exhaust stream to the point where the catalytic converter becomes clogged.

What to Do if You Put Diesel in a Gasoline Powered Car

If you discover that you have mistakenly put diesel in your gas-powered car, do not attempt to fix it yourself. You may believe that adding additional gasoline to dilute the diesel or running the tank dry would solve the problem, but both of these “solutions” will just make it worse.

Adding gasoline will not dilute the diesel fuel. This will just lead to whatever gasoline you add being contaminated. On the other hand, running the tank to empty will move the diesel through the engine and cause even more damage.

The best thing you can do is call a tow truck right away to bring your car to a repair so the fuel can be drained. No matter what, do not try to start the car, since this will cause the diesel to move through the engine, making repairs considerably more complex and expensive.

The longer diesel remains in your gasoline engine, the greater the damage it will do. The sooner you can remove diesel from your vehicle’s tank, the better it will be for its long-term health.

Once your vehicle arrives at the mechanic, the diesel will be drained and the tank will be flushed with gasoline several times to ensure that all diesel has been removed. They will then fill the tank with standard gasoline and start the vehicle to ensure proper operation.

When the mechanic starts your vehicle, there may be some smoke; this is typical if you attempted to start the car yourself. It’s simply the engine burning off any diesel residue that may still be in circulation apart from the fuel tank.

Repair Price

Repairs may be costly and depend on a variety of factors such as the diesel-to-gasoline ratio, the duration of time your vehicle was operating, etc. In general, a simple fuel flush should cost between $50 and $100 if the vehicle was not started, and between $1,500 and $2,500 or more if the vehicle was started. If the damage is severe enough, the repair bill may exceed the car’s worth.

You may be able to make an insurance claim for the repairs, but most policies won’t cover damage caused by the driver using the wrong fuel. Therefore, if you want to avoid a costly repair bill, it’s best to just be careful not to put diesel in your car in the first place.

How To Avoid Pumping Diesel Into Your Car

The color of the handle at the gas station is the primary indicator that you are dealing with either diesel or gasoline. Generally, in the US, diesel pump handles are black, whereas gasoline pump handles are green and may feature octane rating cards on top. Diesel fuel pumps have nozzles with a wider diameter than gasoline fuel pumps, so no matter how hard you try, you will not be able to place the diesel pump nozzle into the fuel neck of your gasoline vehicle.

Gas stations and car companies put all of these measures in place to prevent you from using the wrong type of fuel in your vehicle and causing damage to your vehicle. Since it’s practically impossible to fit a diesel nozzle into a gasoline car, the most common way diesel ends up in your vehicle is by jerry cans. If you store a can of diesel in your garage, be sure it has a different color, label, and storage area than conventional gasoline cans. This will prevent the danger of putting diesel fuel in a gasoline-powered vehicle.


Diesel is not made for gasoline engines, and vice versa. If you accidentally put diesel in your gas powered car, do not turn it on. Call a mechanic right away and have them drain the diesel. This way, you can avoid causing permanent or expensive damage to your vehicle. 

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