What Happens if You Put Diesel in a Gas Car or Gas in a Diesel Vehicle?

At most gas stations, diesel fuel nozzles have a different colored handle and a larger-diameter filler pipe than gasoline nozzles. Yet some drivers manage to put diesel fuel in their gas-powered vehicles and vice versa—and those slip-ups can be costly.

If you’ve made this mistake yourself (or you know someone who has), you’ll want to know the ramifications of the error, as well as what you should do next.

What Happens if You Put Diesel in a Gas Engine?

Most diesel fuel pump nozzles have a larger diameter filler pipe than gasoline nozzles, making it tough to put diesel in a gas engine. Still, some drivers manage to fit diesel nozzles into gas tank filler necks.

What might happen if you put diesel in a gas engine and drive the car without realizing your mistake? If you only add a couple of gallons of diesel fuel to a gas tank that’s at least half full, the engine will usually continue to run but run poorly.

But if you add a significant amount of diesel fuel to the gas tank, in most cases, the car will only run until the gasoline in the fuel lines is depleted. The vehicle will then quit because gasoline engines cannot combust diesel fuel.

At that point, you’ll need to have the vehicle towed to a repair shop so that a professional can drain the fuel tank and flush the fuel system. In some instances, the repair process may involve costly disassembly of major components.

It’s also worth noting that running diesel fuel through a gas engine has the potential to cause hydrolock—a condition where incombustible liquid enters the engine’s cylinders, reducing their overall volume. Such a scenario usually results in extensive internal engine damage.

What Happens if You Put Gas in a Diesel Engine?

Gasoline nozzles tend to have smaller diameter filler pipes than diesel nozzles. Because of this, it’s easier to put gasoline in a diesel-powered vehicle than the other way around. Some newer diesel-powered vehicles have misfuelling protection devices, but most older models do not.

Putting gasoline in a diesel fuel tank can be an extremely costly mistake. Although diesel-powered vehicles may run well on some alternate fuels, such as biodiesel, they should never be run on gasoline.

Adding only a small amount of gas to a diesel fuel tank might not cause any major problems. But if you put a significant amount of gasoline in a diesel-powered vehicle, there’s a good chance the fuel will ignite at the wrong time in the engine’s combustion process. When that happens, vital (and costly) internal engine components can suffer damage.

What’s more, gasoline does not have the lubricating properties that diesel fuel has. Running gasoline through a diesel fuel system can quickly damage major components, such as the high-pressure fuel pump and fuel injectors.

What Should You Do if You Put Diesel in a Gas-Powered Car or Vice Versa?

If you realize you put diesel in a gas-powered car or vice versa, do not start the engine for any reason (not even to move your car away from the fuel pump). Instead, to avoid damaging your vehicle, have it towed to a repair facility to have the fuel tank thoroughly cleaned.

How To Avoid Putting the Wrong Type of Fuel in Your Car

These days, most gas stations make it fairly easy to avoid putting the wrong type of fuel in your car. The nozzle handles are color-coded—diesel is usually green, while gasoline (regular, mid-grade, and premium) is usually black. Also, most diesel nozzles have a larger diameter filler pipe than gasoline nozzles do.

There are, however, some older gas stations that might not adhere to these standards. That’s why you should always read the label on the pump to ensure you’re putting the right fuel in your vehicle.