Corvair Forum

What Happens If You Put Diesel in a Gas Engine?

April 7, 2015
With diesel-fueled cars growing in popularity, most gas stations are starting to sprinkle in diesel pumps among the standard gasoline ones. I know I've been caught off-guard a few times and accidentally pulled up to the wrong pump without paying attention. Fortunately, I've noticed the difference before lifting the nozzle into my tank, but not everyone is so lucky to stop there.
So what happens if you accidentally add diesel fuel to a gas engine? In general, your car will turn out a sluggish performance before it stops running altogether. You might have heard horror stories from a guy, who heard from a friend, that your car will never work again. That isn't necessarily the case. As long as you fix the problem immediately, putting diesel fuel in a gas engine won't always cause permanent damage. Before we figure out how to solve this problem, let's take a look at how diesel fuel affects a gas engine.

Gas vs. diesel engines

Before you panic about making this mistake, keep this in mind: diesel nozzles usually can't fit into new gasoline tanks. Also, diesel has a distinct smell that's very different from gasoline. However, if you don't detect the smell and somehow jam the diesel nozzle into your gas tank, you should know this key difference between a gas and diesel engine:
Gas Engine: Since gasoline is blended with chemicals to avoid self-ignition, this type of engine runs a vehicle by using spark plugs to ignite gas and air.
Diesel Engine: A diesel engine doesn't have spark plugs because diesel fuel can ignite on its own with highly compressed hot air.
Diesel fuel doesn't need assistance to ignite, and it has a thicker consistency than gasoline. As a result, diesel can jam a gas engine's fuel injectors, filters and lines. Since a gas engine doesn't give off the necessary heat and pressure for diesel to combust correctly, this can cause severe timing and cylinder issues. Your vehicle might start and run for a while, however its performance slowly slips, and the car eventually stops running.

How to remove diesel from a gas tank

So now what do you do? It depends on how much diesel you put in your tank. If you caught your mistake early on, filling the rest of the tank with mostly gasoline might be an adequate remedy. When you fill the majority of your tank with diesel, it's a whole different story.

The first step is to stop your car and have it towed back home. You need to fix the problem immediately, as the longer diesel sits, the more damage it can do to the fuel system, engine and injectors. Next, use a siphon pump to remove the diesel from the tank and fill it up with gasoline. In some cases, it could take a while for your vehicle to start up, and the ride might be bumpy until all the diesel naturally flushes out.

The other solution, and most times the safest one, is to call a professional. A mechanic will properly flush out the entire fuel system and clean up the surrounding parts. In some cases, the spark plugs, engine gaskets and filters might need to be replaced if they were seriously affected by the blunder.