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Diesel vs Gas: What's the Difference?

When comparing diesel and gas, it's obvious that the two are different. Consumers can see and smell the difference — diesel fuel is, in fact, heavier and oilier, and it evaporates more slowly than gas fuel.

In the past, diesel engines were branded as slow, loud, and smelly. The result was the improvement of diesel engines, and subsequently, gas engines too.

The evolution of both diesel and gas engines made the differences between them less significant, but both still exist. Let’s compare the two based on a few important factors and see what sets them apart.

How Do Diesel and Gas Engines Work?

Both diesel and gas are internal combustion engines, which means that the fuel mixes with air that goes into the engine. This air and fuel mixture is then compressed and combusts.

This process converts the fuel's chemical energy into mechanical energy. However, one of the biggest differences is how these two fuels ignite in the engine.

In a gas engine the air and fuel mix and become compressed by pistons. The fuel is then ignited by spark plugs.

In contrast, in a diesel engine, there are no spark plugs. The air is compressed and the fuel is injected. As the air is compressed, it heats up making the fuel combust.

Diesel engines need to be maintained on a regular basis. If not, they may run into problems. Repairing a diesel engine is usually more expensive than repairing a gas powered one.

Which is More Powerful?

Before we delve into the matter, we need to explain two important terms in this field: torque and horsepower.

Torque is defined as a rotating or twisting force that may or may not result in motion. When the object is moved it is defined as "work." Meaning the more torque a vehicle has, the more work potential it has.

Horsepower is unit used to quantify the work of an engine, or the rate at which the work is done. It is measured with an instrument called a dynamometer or more commonly referred to as a "dyno."

In mathematical terms, H = (T x RPM)/5252. H is horsepower, T is pound-feet, RPM is revolutions per minute, and 5252 is a constant.

Both torque and horsepower are important. For example, a lot of horsepower with not a lot of torque results in a slow to get going vehicle. Remember, torque is what sets the vehicle in motion.

This is why diesel engines are used for tractor trailers. They are great for moving heavy loads because of their huge torque at lower speeds. With that said, their horsepower is lower than gas engines because they don't rev very high. This is why you don't see a many sports cars with diesel engines.

Price Comparison

We can go on and on about the price of fuel in different countries, but the bottom line is — even though diesel used to be cheaper, today it costs about the same as gas. The price will eventually rise even more, due to the increase in worldwide diesel demand. In other words, if we compare the prices of diesel and gas prices, you won't see a huge difference.

The initial costs of diesel vehicles is usually higher than gas though. This is because of emissions standards in countries like the US and availability of gas vehicles.

Prices as of 4/22/19. Chart from

You might be wondering why people opt for diesel then. They cost more upfront and their fuel prices are greater. While their fuel costs more, they are more efficient at burning the fuel. Diesel contains more usable energy than gasoline, which means that you need less of it in order to achieve the same MPG.

On the other hand, diesel engines will react to poor fuel quality. If you use a fair amount of bad/dirty diesel, you can cause real damage to the fuel injection system and will likely have to pay a lot of money to repair it.

Diesel engines are also “high maintenance” and require fuel additives in order to maintain healthy engine performance. We use high maintenance loosely here because diesel engines are built to last. Using a fuel additive is as simple as pumping gas.

In terms of pricing, there are definitely trade-offs.

Environmental Concerns

The United States has more strict standards when it comes to emissions testing. In years past, Diesel was a culprit for increased air pollution. You might remember Dieselgate in 2015 where the EPA issued VW a notice of violation of the Clean Air Act.

The problem with diesel is the incomplete combustion of fuel. This usually includes numerous chemical elements. A lot of these elements can have a large negative impact on the environment.

Diesel emissions of NOx (nitrogen oxides) lead to the creation of ground-level ozone. However, over the past forty years, companies have made a lot of progress in regard to fuel cleanliness.

These days, diesel runs rather clean. Most of the sulfur and soot that diesel produces has been removed from the fuel. There is also further filtration to the exhaust that make them the standard of clean vehicles. Some diesels use a DEF or "diesel exhaust fluid" additive that is used to treat diesel exhaust and make it cleaner.

We also need to mention bio-diesel. It is an alternative to diesel fuel, and it is ready to use with a few modifications. It is a fry or vegetable based oil that can be used in conjunction with regular diesel.

Final Thoughts

As we’ve noted above, there are differences between diesel and gas. Nowadays, companies put in a large amount of effort so that those differences are not as prominent.

It is believed that cars on gas work better in the city and for shorter trips, whereas diesel fuel is better for longer journeys and highways. Diesel fuel is also more efficient when it comes to fuel cost since it contains more usable energy than gas. On the other hand, repairing a diesel motor can be very expensive, and diesel engines are more sensitive to the poor quality of the fuel. Diesel is a workhorse though and their engines are built to last.

Gas engines are great for speed lovers, but gas and diesel can both be powerful. Years ago, people considered gas more environment-friendly of the two. But today, regulations in most countries have reduced emissions of diesel and gas to a similar level.

Both diesel and gas have advantages and limitations. At the end of the day it comes down to consumer preference.


Richard Reed
I've been a General Manager of a moving company and I've also been a Professional Mover for over 30 years. I've driven flat beds, reefers, dropdecks, moving vans, heavy machinery, etc. In my time as a Mover I've driven over 1,000,000 safe miles. My days of moving and driving truck are past me but The Vehicle Lab allows me to share the knowledge I've gained over the past 40 years.

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