Looking to purchase a new vehicle, but can’t decide whether you should go with a diesel or gas engine? While both fuel types are petroleum-based, they have significant differences in use, as well as in how their respective engines operate.
In this article, we’ll cover the major differences between diesel and gasoline engines, comparing how they stack up when it comes to fuel efficiency, durability, overall expense, and more.
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Diesel fuel vs. gasoline fuel
The first difference between diesel and gasoline is, as you might expect, the fuel itself. While both begin as crude oil—that is, petroleum—extracted from the earth, the subsequent refining process separates them into two types: gasoline and diesel.
Gasoline goes through a more involved refining process and is subsequently thinner and more acidic than diesel, but also harder to burn. Chemically speaking, gasoline consists primarily of three hydrocarbons: paraffin, aromatics, and olefins.
Diesel fuel, on the other hand, is less refined: it’s thicker, has more energy density, and evaporates slower than gasoline. Its chemical makeup is primarily paraffin, aromatics, and naphthenes.
It is these differing properties and concentrations of hydrocarbons that ultimately result in different engines for diesel and gasoline fuel.
How engines work
At a base level, diesel and gas engines operate in much the same way. They both use internal combustion and small, consecutive explosions to turn their respective fuel sources into energy, thus giving the vehicle momentum.
The main differences between the two engines are how they actually go about producing explosions.
In a diesel engine, the air is drawn into the machine and then compressed by pistons, an action that causes the air to heat up. When diesel fuel makes contact with this hot air, it ignites, setting off a series of controlled explosions that move the pistons and rotate the crankshaft, transferring that energy into movement.
In gas engines, the fuel is first mixed with piston-compressed air and then ignited by a spark plug, producing an explosion that fires the pistons, which then rotates the crankshaft, giving the vehicle momentum.
Diesel vs. gas engines
Now that you know the differences in how diesel and gas engines operate, you need to know the differences in the life expectancy, power output, and fuel efficiency between diesel and gas.
Differences in life expectancy
In most cases, you’ll find that diesel engines—and diesel fuel itself—are much more durable than their gas-guzzling counterparts, giving them a longer life expectancy. On average, diesel engines are capable of around 250,000 to 300,000 miles, while gas engines usually clock out around 150,000 to 200,000 miles.
This is mostly due to engine construction, as diesel engines—and all their components—are simple, robust, and built to support continuous use. Gas engines, on the other hand, are more complex and involve the precise cooperation of many small parts—parts that wear down from the repetitive stop-and-go conditions to which most gas vehicles are subjected.
Differences in power output
For the most part, an engine’s power output is determined by the combination of two forces: torque and horsepower. Torque is a measurement that refers to the amount of twisting force on an engine’s driveline and is what actually gets a vehicle moving. Horsepower is simply the measurement of power produced by an engine and helps determine speed.
Gas engines typically have high horsepower and low torque, which means they may be slower to get moving but are capable of greater speed. Diesel engines, on the other hand, are usually high torque and low horsepower, which helps them carry heavier loads for long periods.
Differences in fuel efficiency
On average, diesel is 20% more efficient than gasoline. This is primarily due to its higher density and higher compression ratio, which allows the engine to produce more energy while consuming less fuel, as compared to a gas engine.
So, diesel engines require less fuel to do the same amount of work as gas engines because diesel has a slower burn rate. Similarly, diesel’s high compression ratio allows it to burn better, resulting in higher energy production.
Key Takeaway When it comes down to it, diesel engines tend to have a longer life expectancy and better fuel efficiency than gas engines, though this comes at the sacrifice of horsepower for higher torque. Gas engines, on the other hand, usually have low torque and high horsepower.
Cost of ownership: diesel vs. gas
After everything that’s been said about durability and fuel efficiency, it may seem as though diesel engines will cost you less than gas engines, but this is not necessarily the case.
Though diesel engines are more durable and require less frequent repairs, their fuel is more expensive, and the initial purchasing price of a diesel vehicle is usually far greater than that of gas vehicles.
Additionally, diesel vehicles are much more costly to service and repair—their fees are almost double that of the same servicing or repairs performed on a gas engine.
So when you factor in the additional selling cost of a diesel engine, compounded by higher fuel costs and higher servicing/repair costs, the overall cost of ownership for a vehicle that takes diesel will be slightly higher than that of one that takes gasoline.
Diesel vs. gas pollution
There exists much debate over whether burning diesel or gasoline produces more pollutants per mile, but science tends to put diesel as emitting a slightly higher percentage.
That being said, it’s true that—on average—diesel emits lower amounts of carbon dioxide than burning gasoline does. Unfortunately, this is offset by the fact that diesel engines are capable of producing 25 to 400 times more mass of soot and sulfur per mile.
However, recent standards enacted by the Environmental Protection Agency have required a major reduction of sulfur parts per million in all diesel manufactured or sold in the United States. This has led to the adoption of Ultra Low Sulfur Diesel (ULSD) in all vehicles from the model year 2007 and onwards.
When paired with advancements in exhaust emission control systems, newer diesel engines using ULSD are capable of greatly reducing their emissions, with some burning cleaner than gasoline altogether.
Key Takeaway Depending on the vehicle’s use, gas engines can be more expensive than diesel in the long run, even though they have a lower initial cost. Diesel engines, on the other hand, usually emit more pollutants, though it is possible for them to run cleaner than gas engines.
Deciding which is right for you
Now that you know the differences between diesel and gas, you can decide which would better suit your lifestyle. If you require a vehicle that’ll last a long time and can regularly carry heavy or large loads—a truck, for example—you’ll probably want to go with a diesel engine.
If you only need a vehicle for getting from one place to another—taking kids to school, driving to and from work, etc.—and anticipate a lot of city or urban driving, a car with a gasoline engine will most likely be a better fit.
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Is diesel better than gas?
This is a tricky question, and it depends on who you ask as they are primarily used for different purposes. If you just need a car that gets you from place to place, a gas engine is probably better for you. If you need a vehicle that is highly durable and can reliably carry heavy loads, a diesel engine is the better option.
Why is diesel more expensive than gas?
Diesel is more expensive than gas for several reasons, with the most obvious being that diesel fuel is subject to a higher federal tax. Diesel also tends to be more expensive because there is stronger demand for it internationally, as most European countries and many developing companies favor vehicles that run on diesel.