The Difference Between Gasoline and Diesel Engines

Every car has an engine, but not every car has the same engine. Sounds simple, and perhaps overly philosophical, but it’s true. And the two most popular kinds of engines are gasoline-powered and diesel-powered engines. But what’s the difference, are the two interchangeable, and what are the benefits of each?

Four Cylinder BMW Gasoline Engine And Diesel Engine
BMW Gasoline Engine (left) And Diesel Engine (right) | BMW

What’s the difference between gas and diesel engines?

Both gasoline and diesel engines are known as four-stroke engines. Simply put, the fuel and air are injected into a chamber. That air and fuel are compressed by the piston pushing up and ignited. The explosion of that fuel pushes the piston back down, and then when the piston goes back up, all the exhaust is pushed out. The cycle repeats until you run out of gas, which is hopefully never.

But that third step, when the fuel is ignited, is when things start to differ. A gasoline engine uses something called a spark plug. Think of it like a tiny taser that creates a spark to light the gas/push the piston down. If you have a four-cylinder engine, you have four spark plugs.

Diesel engines don’t have spark plugs. Instead, the air and fuel are much more compressed. And that rapid compression generates heat, which lights the gasoline rather than an external spark. That’s the simple, SparkNotes explanation. But if gasoline engines and diesel engines use the same four-stroke process, why can’t they use the same fuels.

What’s the difference between gasoline and diesel?

A man pumping gas
A man pumping gas | Indranil Aditya, NurPhoto, Getty Images

There are two main differences between gasoline and diesel: thickness and combustibility. The former is fairly easy to understand. Gasoline is much thinner than diesel, whereas diesel is similar to oil in consistency. But despite the richer mixture, it’s actually less combustible than gasoline. Not that it wouldn’t catch fire if you held a match to to the fuel, but gasoline would light much faster.

With that said, don’t ever use diesel fuel in a gas engine or gasoline in a diesel engine. Unless you want to destroy the engine, in which case go ahead. Putting diesel in a gasoline car would clog up the fuel pumps and injectors, which weren’t designed to handle the heavy mixture.

Now, diesel engines are incredibly durable, capable of running on different fuels such as biodiesel, Dimethyl Ether (a key ingredient in hairspray), and even used vegetable oil. In fact, diesel engines were originally designed to run on peanut oil (according to Auto Evolution), a cheap and accessible resource to help stimulate an automotive boom worldwide. However, they can’t run on gasoline.

This is partly because all the aforementioned fuels, and diesel itself, are closer to oil. They have lubricating qualities that keep the engine operating silky smooth as the diesel flows through it. In other words, if diesel fuel didn’t have that lubricating quality, it’d gunk up the engine. Gas is just gas, it wasn’t meant to lubricate anything, which would damage the parts and total the engine.

So don’t mix up the two, that’d be a nail in the coffin for your car. But when you put the right kind of fuel in the right engine, diesel to diesel and gas to gas, they have some distinct advantages.

Which is better: gasoline or diesel?

Gasoline Powered Supercar and Diesel Powered Truck
Gasoline Powered Supercar and Diesel Powered Truck | Martyn Lucy/Paul Weaver via Getty Images

Well now, that’s a loaded question. Deciding which is better all depends on what you’re looking for in a car. Both engine choices are great at their respective jobs, but you wouldn’t want to bring a diesel to a gas fight.

The advantage of a gasoline engine is that it can be smaller while still operating at a higher RPM, whereas diesel engines are big and can only go so fast. Gasoline engines are also cheaper to maintain, and the fuel they use is more readily available across the country. And if you’re into saving the environment, but can’t go electric yet, then gasoline is also the cleaner option.

Diesel engines, on the other hand, run forever. They might be loud and gurgly, unlike gasoline engines, but they’re the go-to option for long-distance big rigs and school busses. If you give them the fuel, they’ll just keep going. They also tend to be more torquey, capable of pulling heavier loads. This explains why they operate quite happily and powerfully at low RPMs.

Long story short, if you’re looking for high speed and performance, you’ll want a gas-burning engine. But if you need to tow, or go on long road trips, then a diesel is the better option.

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