If you drive a vehicle that requires gasoline you probably don’t think much about diesel fuel. That is unless it’s time for a fill up at the local gas station. You may veer away from the dedicated pump that is just for diesel or you may pull up to a pump that has diesel right next to gasoline with varying octanes.
Have you ever wondered what the difference between diesel and gas is? After all, they are both fuels.
What happens if you put diesel in your gas engine or vice versa?
How Diesel and Gasoline Engines Create Power
To understand how each fuel is used by their respective engines, it helps to understand how the combustion process works. Both diesel and gasoline engines utilize the same concept when it comes to using fuel.
Both are internal combustion engines that are made to convert chemical energy from fuel into mechanical energy that forces pistons to move up and down within the cylinders. The pistons, connected to the crankshaft, generate motion that creates the power to propel the vehicle.
Diesel and gasoline engines are designed to convert fuel into energy by small controlled explosions known as combustions. The only difference between the two is how the explosions occur.
Gasoline engines use a perfect mix of fuel and air that are compressed by the pistons and ignited from the sparks created by spark plugs. Conversely, in diesel engines the air is compressed before the fuel is directly injected into the combustion chamber. Diesel engines do not need spark plugs because the air that is compressed creates a high compression ratio and heats up, causing the fuel to ignite.
Diesel Fuel versus Gasoline
Gasoline and diesel are both fuels that start off as mined crude oils that are refined into various kinds of fuels. Diesel fuel can often cost less simply because the refining process is easier, though in recent years diesel prices have steadily risen due to emission regulations. The texture of diesel fuel is thicker and more oily and due to its weight, takes longer to evaporate compared to gasoline. Diesel also has a higher boiling point than water. 
Modern diesel engines get high marks for their MPGs. Some diesel engines can produce better fuel economy by up to 30% compared to their gasoline counterparts. Diesel engines also perform better by increasing power, provide better acceleration, and are more environmentally friendly.
Because diesel engines are more efficient, they emit less carbon dioxide in comparison to gasoline engines. What’s more, many newer diesel engines are equipped with diesel particulate filters that prevent soot from exiting through the exhaust.
How to Tell the Difference Between a Gas and Diesel Car
In the past you could tell the difference between a gas or diesel powered car simply by the sound it produced. Engines in diesel cars produce a rumbly, tractor sound compared to a smoother engine sound produced by gas engines. With all the advancements made with computerized systems, though, modern diesel vehicles are much quieter.
Here are three ways to tell if a car uses gas or diesel:
- Look under the hood. Look at the engine and identify whether there are spark plugs, a throttle body, or a mass air flow sensor. Diesel engines do not have spark plugs and some older models may operate without the throttle body or the mass air flow sensor.
- Check the Fuel Cap. The little door that houses access to your fuel tank should be labeled with ‘Unleaded Gasoline Only’ or ‘Diesel Only’ to indicate what kind of fuel the vehicle utilizes. You can also check the size of the fuel filler neck. A gas vehicle’s fuel filler neck is more narrow compared to the thicker and wider opening of the diesel pump nozzle. If you have to force the nozzle into the fuel filler neck, you’re likely using the wrong fuel.
- Vehicle Name. Cars produced with a diesel engine are most likely to have something in their name to indicate it’s a diesel engine. The vehicle’s model will often have a ‘D’ at the end. For example, a BMW 540d indicates it’s a diesel engine. Trucks typical have diesel displayed in multiple areas on the vehicle.
What Happens if You Put Diesel in a Gas Engine?
Gasoline engines are not meant to combust diesel fuel, forcing the car to stop running. Putting a couple of gallons of diesel in a gasoline engine may not be as harmful as a full tank. The car will run poorly, smoke, and likely stop running. If the entire tank is filled with diesel, the fuel pump, fuel filter, fuel lines, and other components may be permanently damaged.
What Happens if You Put Gasoline in a Diesel Engine?
If you mistakenly add gasoline to a diesel engine, you want to avoid turning the car on all together otherwise you may be faced with severe and irreversible engine damage. The vehicle will need to be towed to an automotive center before the engine is turned on.
In either case, if you notice you’re putting the wrong fuel into your vehicle’s tank, immediately stop adding fuel, avoid starting the car, disconnect the battery, push your car away from the fuel pump, and have your vehicle towed to a trusted technician so that the tank can be drained, and the fuel lines flushed. If you’ve started driving and realize you’ve put the wrong fuel in your tank, pull over, turn off the engine, and call for a tow truck immediately before any further damage occurs.
