Diesel vs. Gasoline: All You Need to Know

Diesel and Gasoline are both petroleum products. Despite the same origin, they have significant differences in their use. Diesel is the fuel for big machinery that demands more torque over horsepower. In comparison, gasoline is a lighter fuel that is used for vehicles needing speed over brute strength.

However, the difference between both is a lot more than just power and torque figures. Read on as we discuss the difference between Diesel and gasoline, including factors like durability, fuel efficiency, and reliability.

Diesel and gasoline are both refined from crude oil. However, gasoline is more refined than Diesel. This makes gasoline thinner in density and more volatile. So, in practical use, gasoline burns faster, which allows it to produce more power or horsepower.

Whereas Diesel fuel is thicker in density, it evaporates more slowly. It has a higher energy density, which means that 20% more energy is produced from Diesel than the same amount of gasoline.

This is why Diesel engines are favored in big machines as they can produce more energy at lower RPMs and provide more torque. In contrast, gasoline engines are used in lightweight vehicles that need less torque and more horsepower to go faster.

Both Diesel and gasoline are fuels that use internal combustion to produce power. In a combustion engine, fuel is burnt by causing an explosion in a closed space (the combustion chamber). As combustion happens inside the engine, it pushes down the piston, which then moves the crankshaft and then ultimately moves the wheels.

While both engines use the same concept, it is the process of combustion that makes the difference.

In gasoline engines, the fuel is first mixed with air and then compressed by the piston. Then a spark plug creates a spark to cause an explosion (combustion). The explosion then again moves the piston, which moves the crankshaft and ultimately moves the wheel.

A Diesel engine, however, doesn’t need spark plugs for combustion.

Diesel engines work on a system called compression-ignited injection. Unlike gas engines, where a simple spark is needed for ignition, Diesel fuel first needs to be vaporized. Then it is sent to the combustion chamber, where it ignites at a high temperature.

Compressed air is used to increase the temperature of the combustion chamber. As the piston compresses the air, it gets hotter due to pressure. The hot air, when mixed with vaporized Diesel, ignites, and combustion happens. A glow plug is used with some engines to increase temperature.

Diesel engines have a high compression ratio which allows them to be more efficient than gasoline. Meaning they can produce more energy compared to gas.

In general, Diesel engines are considered more durable than gasoline power plants. That’s one reason why it’s common to see so many Diesel work trucks. Comparatively, a Diesel can operate for many more miles than a gas engine before needing maintenance and repair.

In addition, a Diesel engine’s life expectancy is around 250,000- 300,000 miles. How many gas engine vehicles do you come across with this kind of mileage? The reason behind the massive difference in durability is both the engine design and the fuel type .

Diesels are big engines with big cylinders, large crankshafts, strong pistons, and multiple gears. These power plants are simple and work off of basic gear operations. Further, Diesel engines are made with heavy-duty materials to support continuous operation. Since engine gears are mostly fixed at a set place, there is limited movement and reduced wear and tear.

Gasoline engines, however, are complicated pieces of engineering. Working mostly on chains and belts, they use hundreds of small parts that require more precision. Regular stop-and-go operations add engine stress which increases wear and tear.

Despite being a denser fuel, Diesel has the consistency of light oil. This means that it continuously lubricates the cylinder over and over again as it moves around. Also, due to the bigger engine size, the oil can move more freely inside, allowing it to lubricate components more easily.

The viscosity of Diesel also decreases with temperature; it gets less dense at high temps. And since it’s also easier to burn, it reduces a Diesel engine’s overall wear and tears.

On the other hand, gasoline is more of a solvent; it’s more acidic when compared to Diesel. So as gasoline burns inside, it causes corrosion making the engine surfaces rougher. This increases the wear and tear inside the gasoline engine.

Another major difference between Diesel and gasoline is fuel efficiency. Diesel vehicles are generally more fuel-efficient than gasoline cars due to thicker density, low rpm performance, and higher compression ratio.

As mentioned before, Diesel is 20% more efficient than gasoline. Its thicker density allows it to produce more energy with less amount of fuel. Also, a Diesel engine can have the same amount of power as gas but at a lower RPM. In other words, a slower rate of burning fuel for the same output.

Then there is the higher compression ratio which is directly related to thermal efficiency. The higher it will be, the better the fuel will burn. This means more rich explosions will happen, and more energy is produced.

However, a gasoline engine can never reach as high a compression ratio. If this did occur, excess heat would ignite the fuel resulting in engine-damaging uncontrolled explosions. So, gas engines require a low compression ratio which results in less efficient combustion.

How each engine type is used also affects fuel economy. Diesel engines are often used in big rigs that usually travel on highways. Gasoline engines are used by daily drivers that travel in the city. This stop-and-go use burns up more fuel.

The cost of ownership of a Diesel vehicle initially seems lower. Diesel cars are more fuel-efficient, are more durable, and need less maintenance. Diesel engines are hard to break. In fact, a diesel engine can easily last 20-30 years before needing major repairs.

On the other hand, the Gasoline engine consumes more fuel, needs more frequent maintenance, and may need more attention after 150,000 miles.

This might make the gasoline engine look like an unwise choice. But over the long run, it is seen that gas engines can get more value than Diesel depending on their use. Because despite Diesel being more robust, it’s also costlier.

Comparatively, a vehicle with a Diesel will cost more at purchase time than the exact vehicle with a gasoline engine. Further, maintenance and repair costs for a Diesel engine go above that of a gas engine. For example, the oil change in a gas engine would be around $20-$40, whereas Diesel oil change costs $50- $70. Diesel engines are larger, so they need more engine oil.

In addition, Diesel engines generally have higher fuel prices. At present, Diesel fuel averages $3.27 a gallon. A Chevrolet Silverado has a city mileage of 22 mpg for Diesel and 19 mpg for gas. Over 10,000 miles, the average fuel cost would be around $1,500 for Diesel and $1,400 for gas (at $3.00 per gallon).

So, considering the additional price for a Diesel vehicle, higher fuel costs, and more expensive servicing, the cost of ownership for Diesel is higher than that of gas over ten years at 10,000 miles/year.

Diesel and gasoline engines have their unique advantages. In general, if you drive less than 12,000 miles a year with regular use, then a gas engine will meet your needs. Also, if you prefer driving a car with some “get-up and go,” then you’ll likely want to skip a Diesel.

However, if you drive extensively (15,000+ miles per year), carry heavier cargo, or tow big loads, then a Diesel will make sense. Yes, a Diesel will have higher upfront and fuel costs, but its overall efficiency offsets this. A Diesel is also ideal if you need the engine to run at idle for hours on end.

Check out our extensive collection of used Diesel cars, trucks, and SUVs. Please note that our inventory changes frequently and is subject to prior sales. Be sure to ask us about incoming used Diesel models.

Let the professionals at Trust Auto in Sykesville help you select the right vehicle for your needs. Whether you’re looking for a rock-solid work truck or a comfortable family cruiser, we’ll go over all the details.

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