What Can Happen If You Put Diesel in a Gas Car?

If you’re distracted at the pump, it’s easier than you might think to select the wrong fuel and begin pumping it. There are stations these days that have options for E85, regular, mid-grade, premium, ethanol-free, and diesel, all at the same pump. If you’re having a bad day, pumping diesel into your gasoline-powered car can turn it into a nightmare.

Diesel vs. Gas

Gasoline is a highly refined fuel that is extremely volatile and releases highly combustible vapors. Diesel is closer to oil, though. It is more viscous (thicker) and doesn’t release VOCs (Volatile Organic Compounds) as gasoline does. 

These properties have been designed by the chemical engineers who developed these fuels, and for a good reason: diesel and gas engines work on totally different principles. Both engine types operate on internal combustion, but the difference lies in how they get there. 

Since gasoline is so volatile, engines designed to run on it achieve ignition by means of a spark, which is timed precisely by the Engine Control Module (ECM) to send an electrical charge to the spark plug exactly when the engine is ready. 

Diesel engines achieve ignition through the heat that is generated by compression. There is no spark plug in a diesel engine, and diesel fuel is formulated specifically to work on this compression ignition principle. 

The Consequences

So what happens when you get it wrong? Lots of bad things. 

First, since diesel is thicker than gasoline, your fuel pump will struggle to pump it through the fuel lines. Then, when it reaches your injectors, they will clog and fail. If any diesel happens to make it into the combustion chambers of your gasoline engine, the results could be bad — engine-seizing bad.

The Fixes

The first fix is prevention. You can take steps to make yourself more aware, even when pumps serve video ads that play at a loud volume that shake your teeth and make you forget your name. Just remember: at most stations (except for BP), a green nozzle means diesel.

But if you happen to have already pumped diesel into your tank, it’s still not too late to avert disaster. If you don’t start your engine, you can prevent a major repair bill. 

The easiest fix for diesel in your gas tank is to drain the tank. Most tanks have to be uninstalled from the vehicle to accomplish this (dropping the tank). But draining it alone won’t do; it must be flushed with fresh gasoline. 

The repair bill could run you a couple of hundred bucks or as much as triple that, but it’s far better than the thousands it would require if you had to replace fuel lines, injectors, and more.

Don’t Get Distracted When Fueling Your Car

Fuel stops are no time to be distracted. The consequences of pumping diesel into your car could cost you hundreds, if not thousands, of dollars to fix. Next time you pull in for fuel, make sure to double-check before you squeeze the handle.