Diesel vehicles usually elicit strong feelings in almost everyone from car buffs to the automotive industry: they’re either loved or hated. Some claim they’re more efficient and that they offer better performance, while others say they’re dirty machines that pollute the environment. Both claims are somewhat true. We’ve done the in-depth research and will leave it up to you to decide if diesel cars are better than gas cars. 

Let’s pop the hoods and examine how each engine operates.

How Does Each Engine Work?

There are a few key differences between gasoline and diesel engines. However, both engines operate on the same basic concept, which you should familiarize yourself with in order to understand how they work. 

The Four-Stroke Cycle: Stroke by Stroke

Inside an engine cylinder, a piston moves down as an air valve opens. The piston sucks in the air entering through the air valve, while the fuel injector supplies fuel, creating an air-fuel mixture. 

Once the piston reaches the bottom dead centre (BDC), the air valve begins to close. At the same time, the piston starts going up, compressing the air-fuel mixture until it reaches the top dead centre (TDC).

What follows is the so-called “power stroke.” Once the piston compresses the air-fuel mixture, the mixture is ignited, forcing the piston back down the cylinder.

Finally, the exhaust stroke pushes the gases from the ignited air-fuel mixture upwards, through the exhaust valve, into the exhaust, and out of the vehicle. The exhaust valve then closes and the process is repeated.

What’s the Difference Between a Gas Engine and a Diesel Engine?

By pressing the gas pedal on a gasoline-powered vehicle, you’re modifying how much air gets into the cylinder. That’s why gasoline engines have a throttle body and diesel engines don’t. On a diesel-powered vehicle, it’s the other way around: you’re modifying how much fuel gets into the cylinder. 

The biggest difference between the two types of engines is how they ignite the mixture. The compression ratio of a gasoline engine is usually around 10:1, while the compression ratio of a diesel engine can be 16:1 and up. That’s because gasoline engines utilize spark plugs to ignite the mixture, while diesel engines utilize compression and the self-ignition temperature of diesel fuel. Compressing the mixture will increase the temperature, causing it to combust on its own, without an external source like a spark plug. If gasoline engines had a higher compression ratio, the mixture would ignite by itself prematurely.

Another difference between diesel engines and gasoline engines is the air-fuel ratio. Gasoline engines have air-fuel ratios of between 12:1 and 18:1. Diesel engines, on the other hand, operate on a much larger scale: they can have air-fuel ratios ranging from 18:1 to 70:1. 

Is Diesel More Efficient than Gasoline?

It’s relatively well known that diesel engines are more efficient than gasoline engines, but diesel-powered vehicles lose their efficiency over time.

Once crude oil is burned and distilled, products such as gasoline and diesel are the result. Diesel fuel, with a structure of C15H28, is more energy-dense than gasoline, which has a C8H18 structure. Because of diesel fuel’s overall poor quality, it requires additives to improve fuel economy and lessen both carbon dioxide (CO2) and nitrogen oxide (NOx) emissions. Only then can the fuel be sold.

Diesel engines do not have air restrictions in the way that gasoline engines do, resulting in fewer pumping losses. Additionally, diesel engines—especially modern ones—utilize high-pressure fuel injection systems with extremely small holes. That way, diesel fuel is spread out as far as possible into very fine mists, resulting in more power and efficiency as well as less particulate matter and fewer emissions.

All of this results in better efficiency, but due to high-pressure fuel systems and poor-quality diesel fuel, diesel engines lose power over a period of time.

Performance of Each Engine

There’s no better option than diesel when it comes to hauling upwards of ten thousand kilograms. That’s because diesel engines produce much more torque at lower RPMs, meaning you’ll be able to move a heavy object more efficiently. Diesel powerplants also offer impressive acceleration from a standing position as compared to gasoline powerplants.

In terms of horsepower and top speeds, both engine types can be modified to reach extraordinary numbers, so overall, diesel is a better performance option.

Life Expectancy of Each Engine

Generalizing the durability, reliability, and longevity of groups of vehicles won’t result in useful information. There are vehicles on the road with a million kilometres or more running with both diesel and gasoline powerplants.  

However, diesel engines and transmissions must be built out of sturdier and stronger materials in order to withstand the compression and torque. Additionally, diesels operate at a much lower RPM range, meaning that the components and parts wear out less quickly. The downside of diesel-powered vehicles is that the fuel isn’t of a high quality. Needless to say, running low-quality fuel won’t help with the longevity of your vehicle.

Both diesel and gas vehicles can be reliable and can last for millions of kilometres, so long as you give them the necessary attention, keep a tight preventative maintenance schedule, and run high-quality fuel.

Money Savings and Gas Mileage

The general notion about diesel vehicles is that they offer much better fuel economy, but that is only partially correct. A decade to two ago, that was completely true, but because of strict EPA emissions regulations and diesel exhaust filtration systems, diesel fuel economy has gotten drastically worse.

On the other side of the road, we have gasoline vehicles that have seen countless engine advancements and innovations combined with fuel injection improvements that have only improved the fuel economy of gasoline vehicles. 

Diesel vehicles do still offer better fuel economy (especially if you’re using your vehicle for towing and hauling hefty loads), but the difference isn’t as noticeable as it was a decade ago. That said, a fleet of diesel vehicles will save you a lot of money on fuel bills versus gas vehicles. 

In terms of upfront cost, gas-powered vehicles will generally save you a few thousand bucks. There are always exceptions, but diesels are usually more expensive than their gasoline-powered counterparts. 

When it comes to preventative maintenance and repair bills, diesel vehicles require more oil, more frequent oil (and oil filter) changes, and need more attention overall in order to operate correctly. Additionally, diesels usually have a few more parts than gas vehicles that will need repair (including strict emissions equipment).

The general belief is that diesel vehicles will save you more money in the long run. But that might not be the case for certain vehicles, and that’s why you should calculate everything before making a decision.

The Future of Each Engine

A decade ago, diesel vehicles owned more than half of the market share, but it has dropped over the years to where it sits today, at less than 30 percent. The demand for diesel vehicles has gone down, and it’s uncertain whether or not automakers are going to continue producing diesel-powered hatchbacks and sedans. On the other hand, because of a diesel engine’s torque production (and because electric vehicles can’t yet tow large objects), diesel will power pickup and semi-trucks for the foreseeable future.

Gasoline engines will power vehicles for years to come. The automotive industry is nowhere near finished with gasoline-powered engines: the market share of electric vehicles currently sits at just three percent. That number is estimated to rise to 23 percent by 2027, but electric vehicles will most likely replace diesel vehicles first and foremost, bumping only a small percentage of gasoline vehicles.

Environmental Considerations

There is a great deal of confusion about diesel engines and the effect that they have on the environment. Believe it or not, while diesel engines are actually better for the environment than gasoline engines, they’re much worse for humans. 

Diesels are much more efficient and emit less Carbon Dioxide CO2 into the environment. Instead, they emit more NOx than gasoline engines.

NOx contributes to acid rain and ground-level ozone formation that is harmful to humans, to animals, and to the entire ecosystem. CO2 on the other hand, contributes to global warming.

The Best Diesel Vehicles in Canada

In Canada, we don’t have that many options in terms of diesel vehicles, but the ones that are offered might just be great options for you!

Chevrolet Colorado/GMC Canyon. General Motors pickup trucks with a 2.8-litre, four-cylinder diesel powerplant capable of producing 186 horsepower and 369 pounds-feet of torque.

Ford F-150/Super Duty. A pickup truck from Ford that’s powered by a 3.0-litre, V6 diesel engine that produces 250 horsepower and 440 pounds-feet of torque.

Jaguar F-Pace. A classy and stylish SUV with a 2.0-litre, four-cylinder turbodiesel that offers 177 horsepower, 318 pounds-feet of torque, and solid fuel economy.

Jaguar XF. A relatively simple sedan that’s powered by a 2.0-litre, four-cylinder turbo engine that offers 180 horsepower, 318 pounds-feet of torque, and 5.8 litres per 100 kilometres on the highway.

The Finish Line

There’s no clear winner when it comes to whether diesel or gas vehicles are better overall. Each type has its advantages and disadvantages, which you should carefully consider before you settle on one.

Diesel vehicles will provide you with better fuel economy, better durability, and better performance, while gasoline vehicles are better for the environment, give you more options to choose from, and have a brighter future.