Diesel vs. Gas Engines: Key Differences Between Gas and Diesel

Diesel vs. Gas Engines: Which is Best?

Whether you’re buying a new car soon or are thinking about becoming a technician, you might be wondering, “what’s the difference between a gas and diesel engine or is diesel better than gas?"

Both gas and diesel engines are internal combustion engines that convert chemical energy into mechanical energy. The mechanical energy moves pistons up and down inside cylinders, which is used to help create a rotary motion that turns the wheels of a car.

Diesel engines are often preferred in industries like construction, transportation and agriculture due to their durability, power and fuel efficiency. Diesel engines are about 20% more thermal efficient than gas engines, resulting in a 20% increase in fuel economy. Diesel engines have higher torque generation and longer life spans compared to gas engines.

Gas and diesel engines both convert fuel into energy through a series of small explosions or combustions. However, these engines have their differences as well. Gas engines are generally more affordable to purchase initially and produce fewer emissions but have lower fuel efficiency and torque production. Diesel engines have a longer life expectancy and are built to be more robust.

Keep reading to learn all about what makes gas and diesel engines unique, the four-stroke combustion cycle, common misconceptions and more.

Is Diesel Better Than Gas?

Diesel engines have several advantages compared to gasoline engines, often making them the preferred choice, especially in industries like construction, transportation and agriculture. These sectors rely on durability, power and fuel efficiency to run smoothly.

Before getting into what makes these engines different, it helps to know what the difference between diesel and gas fuel is. They’re both mined and begin as crude oil but are separated during the refining process. Diesel fuel is thicker than gas and more energy dense.

One of the most important differences between gas and diesel engines is thermal efficiency, or the work that can be expected to be produced by the fuel put into the engine. A diesel engine is about 20% more thermally efficient than a gas engine. This directly relates to a 20% increase in fuel economy.

Diesel engines are used in a wide variety of equipment and vehicles, anywhere from medium-duty trucks to cruise ships and power generators. They’re used because of their increased fuel efficiency, which results in lower operating costs.

They are also used because of their reliability. A diesel engine runs at a much slower RPM (revolutions per minute) than a gas engine and is, therefore, more durable and long-lasting.

Increased thermal efficiency also translates to more power and torque. Essentially, diesel engines provide a better bang for your buck for the fuel put into them. A diesel engine’s high torque application is very beneficial for hauling, as it helps with carrying heavy loads.

Gas engines, on the other hand, have a much higher volatility point but a lower flash point. The combustion of a gas engine is controlled by a spark. The fuel is compressed with fresh air and once the piston is on top of its stroke and the compression is at what the manufacturer wanted, a spark ignites the fuel and air mixture, causing the engine to run.

A diesel engine does not use a spark. It’s also called a compression combustion engine, which means it has a higher compression ratio than a gas engine. The air-fuel mixture is squeezed so much that it explodes on its own.

Essentially, a gasoline engine is a spark-fired combustion, and a diesel engine uses compression.

Pros and cons of diesel engines

There are pros and cons to using diesel engines. Some of the positives include:

• Higher fuel efficiency, providing more miles per gallon compared with gasoline engines.
• Higher torque generation, making them well-suited for towing and hauling heavy loads.
• Fuel generally has a higher energy density, offering more power and better mileage.
• Longer lifespans due to their sturdier construction and lower RPM operation.

On the flip side, some of the drawbacks to diesel engines can be:

• Often more expensive to purchase initially, the cost of diesel fuel varying and becoming more expensive than gasoline.
• Higher nitrogen oxides and particulate matter emissions, contributing to environmental concerns (although advancements in diesel technology are addressing these issues).
• Higher maintenance requirements for components like fuel filters and emissions control systems.
• Noisier and produce more vibration compared to gasoline engines.

Read: How Does a Diesel Engine Work?

Why is diesel better than gas?

Diesel engines offer several advantages over traditional gasoline engines, making them a preferred choice in certain applications. One key advantage is their efficiency in converting fuel into power, as diesel fuel contains more energy per gallon than gasoline.

This higher energy density results in better fuel economy and mileage for diesel vehicles, making them more cost-effective in the long run. Additionally, diesel engines are known for their durability and longevity due to their robust construction and lower operating temperatures, leading to less wear and tear over time.

The torque output of diesel engines is also higher than that of gasoline engines, making them ideal for heavy-duty tasks such as towing and hauling. Overall, the efficiency, durability and torque of diesel engines make them a favorable option for individuals seeking power, reliability and fuel economy in their vehicles.

Pros and cons of gas engines

Just like diesel engines, gas engines have a unique set of pros and cons. Positives to using gas engines include:

• Generally, more affordable to purchase initially compared with diesel engines.
• Gasoline itself tends to be less expensive than diesel fuel in many regions.
• Quieter and smoother than their diesel counterparts.
• Fewer nitrogen oxides and particulate matter emissions, making them relatively better for the environment.
• Fewer maintenance requirements for components like fuel filters and emissions control systems compared with diesel engines.

Some negatives to gasoline engines include:

• Typically, lower fuel efficiency compared with diesel engines, offering fewer miles per gallon.
• Generally, less torque production, which might make them less suitable for heavy towing or hauling.
• Usually, shorter lifespan compared with diesel engines due to their higher RPM operation and lighter construction.

Diesel vs. Gas Engine Life Expectancy

Diesel engines offer several advantages over gasoline engines.

One of the key advantages of diesel engines is their higher fuel efficiency, typically providing better miles per gallon due to their higher compression ratios and the energy density of diesel fuel.

Another major difference between gas and diesel engines is life expectancy.

When gasoline engines hit the 120,000-to-150,000-mile mark, the cylinders will start to show some wear, which decreases efficiency. Diesel engines, on the other hand, are known for their long-life cycle. Some can last a million miles plus.

While diesel engines are designed similarly to gas engines, the cylinder on a diesel engine has a removable liner. When the engine reaches 200,000 or 300,000 miles, the liner can be replaced without having to replace the entire engine.

Diesel engines run at low RPM but create high torque. A gas engine in a car will turn twice as many revolutions per minute going down the highway as a diesel truck, meaning the diesel truck wears at half the rate of the car, resulting in a longer life expectancy.

Finally, diesel engines are very robust, which allows them to last longer. The castings are built thicker, the cylinder walls are built thicker and the oiling system has a higher volume. Diesel engines are really built for the long haul.

These qualities make diesel engines a preferred choice in industries such as transportation, construction and agriculture where power, durability and fuel efficiency are critical factors.

Diesel Engine vs. Gas Engine

There are a variety of misconceptions out there when it comes to gas and diesel engines. However, as technology advances, many of these misconceptions have proven to be untrue.

Pollution

The government is continually putting stricter requirements on diesel manufacturers when it comes to pollution. 25 years ago, semitrucks on the road were billowing black smoke out of exhaust pipes.

However, thanks to today’s technology and engineering, diesel engines run cleaner than ever before. In fact, many joke that the air coming out of a diesel engine today is cleaner than the air going in!

Noise

One of the first things that might come to mind when you think of a diesel engine is the noise it makes. Modern technology has made it possible to eliminate the loud rumble heard when starting up a diesel truck. In fact, from the inside of many diesel-powered vehicles, you wouldn’t even know if it was powered by a gas or diesel engine.

Cost

Even though diesel fuel often costs more than gasoline, it contains more potential energy. Therefore, less diesel fuel is required to accomplish the same amount of work. Because of this, the overall cost for gasoline and diesel fuel over time comes out to be nearly the same. However, this is dependent on the vehicle, driving style and several other factors.

The Role of a Technician

If you’re considering becoming a diesel technician, you might be wondering if you need to know how to work on both gas and diesel engines. While this isn’t a must, technicians who can work on both have great advantages when entering the workforce.

By having knowledge on both gas and diesel engines, you can become a great asset to a dealership or wherever you decide to work in the transportation industry. Even automotive dealerships have cars with diesel engines, which means they need qualified technicians who can work on their vehicles.

When applying for diesel jobs, understanding gas and diesel engines, as well as knowing how to work on them, can really set you apart and give you a competitive advantage. Additionally, it can provide job security due to the demand for technicians who are trained to work on different types of engines.

Gas and Diesel Engines at UTI

So how does one train to work on gas and diesel engines?

Working on diesel engines requires a specific type of training, which is why many aspiring technicians choose to complete a training program such as Universal Technical Institute’s Diesel Technology program.¹

In this 45-week program, you can learn the basic mechanical functions of combustion engines.⁷ Foundational diesel courses build your base knowledge from the ground up, teaching you how to diagnose, repair and replace gas and diesel engines. From here, you can move on to specialized advanced training on trucks and engines from leading brands.

In the program, you’ll learn topics such as:

• Truck brakes and chassis: Training on complete trucks in a real-world shop environment, you’ll learn to perform service, repairs and electronic diagnosis on foundation and anti-lock brake systems, as well as air brakes and hydraulic brakes.¹⁸
• Truck preventive maintenance: Receive instruction on basic truck wheel alignment procedures and learn how to perform original equipment manufacturer recommended maintenance and Department of Transportation annual safety checks.
• Diesel engines: Learn the principles of operation of four-stroke engines including diesel combustion fundamentals and other characteristics unique to diesel engines.
• Diesel fuel systems: Discover how to safely diagnose and repair mechanical and electronically controlled diesel fuel-injection systems.
• Transportation refrigeration: Learn to service and repair major components on a transport refrigeration unit.

Additionally, UTI’s Diesel Technology program is accredited by the ASE Education Foundation, a nonprofit organization that evaluates technician training programs against standards developed by the automotive, truck and collision industries.¹⁶

Graduates of the program are well prepared to take ASE examinations and can substitute their training for one of the two years of work experience required to become ASE certified. Having specialized training, real-world experience and valuable diesel mechanic certifications can really make you stand out to employers.

Overall, gas and diesel engines have similarities and differences. As the transportation industry continues to evolve due to changes in technology, a new generation of technicians who can work on both types of engines will be needed to step up to the challenge.

READ: Is Becoming a Diesel Mechanic A Good Career Plan?