Home Diagnosis and TroubleshootingEngine Problems What Is A Cummins – Are Cummins The Best Diesel Out There?

What Is A Cummins – Are Cummins The Best Diesel Out There?

by Jordan Harris
What Is A Cummins

Are you looking for a truck with a diesel engine and you’ve noticed the Cummins name all over the internet. So, you are asking yourself what is a Cummins? Well, if that is the case and you want to learn what a Cummins engine is, then you are at the right place because there will be a lot to cover on this topic.

Doing the proper research before you go out there on the market and throw a bunch of money on a truck with a diesel engine is essential. Why I’m saying this? Well, this is the case because trucks with diesel engines are really expensive in comparison to gas-powered vehicles.

This is why you need to be properly informed before you spend this money. You need to find what suits you best. Whether it is a Duramax vs Cummins or Duramax VS Cummins VS Powerstroke. You need to be properly informed about these types of engines and learn what is the best for you. And luckily for you, we learn everything you need to know about the Cummins engine.

First, we will learn what is a diesel engine and how it works. Then we will cover the pros and cons of owning a diesel. After that, we will learn what is a Cummins and the most frequent Cummins engines that you will notice when you look for a diesel truck. We will cover their specs, common problems, and if they are worth it. So, if you want to learn more, follow along.

What Is A Diesel Engine & How It Works?

Now before we dive into the topic of what is a Cummins and learn more about Cummins engines. Let’s first learn more about the basics of diesel engines and how diesel engines work. This is really essential when it comes to understanding what is Cummins. So, let’s cover some of the basics.

So, what is a diesel engine? Well, a diesel engine is an internal combustion engine that is using diesel fuel as its source of energy.

Diesel fuel is a fuel that is very different in comparison to gasoline (if you need to learn more, check out our guide on what color is gasoline). It is far less flammable and it burns very slowly. This gives it a very good characteristic. And that is the fact that diesel can produce a lot more energy than gasoline. And as we all know, energy is the prime mover of everything in this world.

So, diesel engines are in a lot of heavy-duty machinery. These engines create a ton of low-end torque. And by low-end torque, we mean immediate torque. Right from the low RPM band.

These engines are a completely different philosophy in comparison to gas-powered engines. Mainly because they ignite the fuel quite differently.

Diesel engines do not rely on spark to ignite the fuel. But rely on compression. The diesel fuel gets so compressed that ignites by itself. And this is one of the reasons why diesel engines have so much torque in comparison to gas-powered engines.

So, if you plan to purchase a diesel engine for towing, this is the way to go in our opinion. No gas-powered engine can match a Cummins or a Duramax. But what is a Cummins? We will get to that in a bit. But first, let’s learn more about the pros and cons of running a diesel engine.

Pros And Cons Of Running Diesel Engine

As we cleared the basics of diesel engines and learned how they work. We think that now it is time to learn the pros and cons of having a diesel truck.

Knowing these things will be really useful before we jump to the topic of what is a Cummins and understand more about the Cummins brand of diesel engines. So, let’s cover the pros and cons briefly.


Now before we learn what is a Cummins, let’s learn more about the pros of having a diesel engine. And frankly, there are a number of pros when it comes to these engines. So, let’s begin discussing them.

The first and biggest pro when it comes to diesel engines is the torque they make. This type of toque is not something comparable to gas-powered engines. When it comes to diesel power, the torque is instant and extremely high. Especially if you have a turbocharged diesel engine.

Nowadays 99% of diesel engines are turbocharged and this process of forced induction basically makes them comparable to gas-powered cars in terms of speed.

Diesel engines are perfect for hauling or towing heavy stuff. A gas-powered engine will really have a hard time performing these tasks but a diesel engine will not break a sweat.

What Is A Cummins

Another pro of running a diesel is fuel efficiency. Diesel engines are really efficient and deliver a ton of power for very little burnt fuel because diesel fuel is more energy-dense than gasoline.

If with a gas-powered truck you get 10 MPG or less fuel economy, with a diesel engine you will get 22 or even up to 28 MPG on the highway. This translates into a ton of money saved on fuel. Especially nowadays when gasoline is so expensive.

And the last pro that we are going to cover is reliability. Diesel engines are extremely reliable since they lack spark plugs and other ignition components that most gas-powered engines have. This reduces the chances of something failing. But what is a Cummins? More on this in a bit.


Now before we cover what is a Cummins, let’s learn more about the cons of having a diesel engine. As you probably know, everything has its pros and cons and so does the diesel. Since if there weren’t any cons, diesel engines would have replaced gas-powered cars a long time ago. Now let’s elaborate on them.

The first con of having a diesel engine is that it is quite more expensive to purchase than a gas-powered engine. These engines are $3,000 or even more in some cases. And this isn’t the price that everyone wants to pay in order to own a diesel engine.

Another con of diesel is the higher price of the fuel. Diesel costs 25 to 50 cents more per gallon than gasoline. So, people don’t want to spend more money on this fuel.

What Is A Cummins

Also, diesel engines are really noisy. If you heard the phrase “It works like a tractor”, then someone probably is referring to a diesel-like type of work. So, you need to be prepared for this. Even though engines now run much smoother than back in the day.

The next con is that diesel engines are expensive to repair. Even though they are more reliable overall when they break repairs are really expensive. The prime parts that often break are the injectors and turbos. These could easily cost you $2,000 or more to replace.

And the last reason why you don’t see diesel vehicles quite a lot on the road is that these vehicles create a ton of NOx particles. These particles are really dangerous. Gas-powered cars are running much cleaner and create far less NOx than diesel. Overall, these are the cons. But what is a Cummins? More on that we will cover next.

What Is A Cummins?

So, what is a Cummins? Well, Cummins is an American corporation that makes one of the best diesel engines worldwide.

Cummins basically has its name all over the history of diesel engines. This is a company from Columbus, Indiana, and is one of the largest producers of diesel engines in the world.

They were founded in 1919 by Clessie Lye Cummins and J. Irwin Miller. They had so much trust in the diesel engines that they even put diesel in race cars in 1950 when a roadster raced in the Indianapolis 500.

Nowadays Cummins focused mostly on engines for heavy equipment. Namely, engines and turbochargers. But they also make generators.

In the truck world, their products are included in most of the RAM lineup. Like the RAM 1500, 2500, and 3500. In addition to this, their engines are used on a ton of semi-trucks and buses out there.

And the last thing to add is that Cummins is focused on reducing the carbon footprint of their engines to a big extent. In only a couple of years, they managed to reduce the CO2 emissions from 842Kt in 2017 to 595Kt in 2020.

It is really good to see that diesel technology is advancing and diesel engines pollute far less than they did a couple of years back.

So, we learned what is a Cummins and a little bit about its history and its applications. But what are the most common Cummins engines out there? Let’s elaborate more on this in the following chapter.

Most Popular Cummins Engines

Now, since we covered what is a Cummins, we can start learning more about the Cummins engines. More precisely the popular Cummins engine that is widely used on light-duty trucks and semi-trucks. Knowing the engines and common problems they have will make your purchase process a lot easier.

5.9 Cummins Engine

The Cummins engine sizes are going from one end to the other and their offer has a choice for everyone. We learned what is a Cummins and now let’s cover the first engine. And that is the 5.9 Cummins.

This engine is one of the most popular engines for light-duty use. This engine precisely belongs in the B series of engines. This is a family of inline engines and they range from inline-4 up to inline 6. And were first introduced in 1984. But they were really upgraded since then.

5.9 Cummins Engine Specs

Nevertheless, the 5.9 is an inline-6 turbo diesel engine that has a displacement of 359cu and was produced until 2007 when it was replaced by the 6.7 that we are going to discuss later on.

When it comes to the 5.9, it is worth noting that this engine is known as the 12 valve. This engine used the Bosch fuel systems. Namely, Bosch injectors and a VE rotary pump also some P7199 inline injection pumps.

Anyone who is into diesel will tell you that Bosch systems are simply one of the best and offer great reliability compared to other systems and this guaranteed that the 5.9 will be one of the most reliable engines around.

It is worth noting that in 1998, there was a new variant of this engine that is known as the ISB. This engine had an upgraded fuel system. It started using common-rail high-pressure direct injection. And implemented 4 valves per cylinder. And this later model was known as the 24-valve Cummins.

Thanks to all these upgrades, the engines from 1998 to 2007 are producing about 325hp and 610lb-ft of torque. Far more than its predecessor. But what about the problems that this engine has? Let’s elaborate next.

5.9 Cummins Common Problems

We learned what is a Cummins, now let’s see what are the common problems with the 5.9 engine. What can you expect from this engine in terms of problems?

Well, we can say that the engines produced until 1998 are pretty much bulletproof. But the 24 valve ISB with a common rail system has a fair share of problems.

1. Lift Pump Failure 1998-2004

What happens is that this engine has a lift pump that goes bad pretty frequently. This pump is basically the one that pulls the fuel from the gas tank and sends it to the high-pressure fuel pump. And when this pump fails, it strains the high-pressure fuel pump as well causing it to fail.

All this was due to the fact that the lift pump was not in the fuel pump but on the engine. And this put a ton of stress on the pump and caused it to fail. After 2004, this pump was relocated to the fuel tank.

2. Leaking Fuel Injectors

The second most common problem that you need to learn after you learn what is a Cummins are the problems with the fuel injectors.

This generation of the Cummins uses common rail fuel injection. This system basically pushes the fuel with a great amount of force. And what can happen is that these injectors could fail if you use diesel that isn’t that clean.

So, what this dirty fuel can do is it can ruin the injectors on your truck. And these injectors cause a lot of money to replace. This is why you need to focus on finding a well-sorted-out example that does not have problems with the injectors. These injectors fail at about 150,000 miles.

3. 5.9 Cummins Other Problems

The next problem that you need to learn after you learn what is a Cummins is the issue with the exhaust manifold bolts. They break from a ton of heat and can cause an exhaust leak.

Other problems include issues with the APPS sensor. This is the accelerator pedal position sensor that is located on the gas pedal. It tends to fail on these engines.

And the last problem is an engine block issue. There are some defective blocks on the Cummins 5.9. These blocks produced between 1998 to 2002 can crack. More precisely the ones that are produced in Brazil and have #53 etching on the side. So, you want to avoid one of these blocks. You just don’t know when it will crack.

6.7 Cummins Engine

We learned what is a Cummins, now let’s cover the next engine. And that is the 6.7 Cummins Engine.

The 6.7 has replaced the 5.9 engine and since 2007 comes as a standard high displacement engine for the Dodge RAM and a lot of school buses around. So, what are the specs of this motor? Let’s cover them next.

6.7 Cummins Engine Specs

The 6.7 Cummins engine as its name implies is 6.7L in displacement. Or 408.2cu. It has a bore of 4.21 inches and a stroke of 4.88 inches. And an overall compression ratio of 17.3:1.

This engine comes with a common rail high-pressure direct injection as a standard. We can say that the common rail system on this engine is more refined and less prone to problems.

The 6.7 Cummins horsepower is between 150hp and 400hp depending on the application, and the torque is rated between 610lb-ft and 1,000lb-ft, also depending on the application of the engine.

What is new for this engine is the new variable geometry turbocharger that was designed to reduce the turbo lag and improve the drivability of this engine. And this engine can be easily regarded as the best Cummins engine because of the good 6.7 Cummins reliability

The 6.7 Cummins weight is about 1,070lbs. This means that this engine is quite heavy.

6.7 Cummins Common Problems

Now as we know what is a Cummins, we can learn more about the problems that this 6.7 Cummins has.

The biggest problem with this generation of the engine is that the DPF is really notorious for clogging up. The DPF is the diesel particulate filter. The one thing that was added to the modern generation of diesel engines.

This filter has the goal to reduce the NOx particles that are released from the exhaust. And it does the job fairly well. But what can happen is that you need to clean it every 60,000 miles or so. There are services that do this job for you and the DPF is good as new once again.

The second most common problem with this engine is the turbocharger failure. The turbocharger failure is common on these because it is a new design. This is a variable geometry turbo. So, the bearings could ultimately fail and cause a ton of issues.

But what is good is that the turbo can be rebuilt for a certain amount of money. There are hundreds of shops doing this type of work.

Another quite common thing on these engines is the head gasket failure on the 6.7 ISB. It is claimed that this is caused by the extremely high compression.

Also, this engine has problems with fuel dilution since it doesn’t have that 7th injector to spray fuel. And the last issue is the EGR cooler problem. EGR issues are really common on diesel engines because these valves end up clogged up and cause problems with the work of the engine. So, these are the issues overall of what is a Cummins.

Facts about Cummins Diesel Engines

  1. A Cummins diesel engine is a superior truck engine that provides horsepower and torque to tow a hefty load and has unmatched durability.
  2. Cummins started manufacturing engines in 1919 at its present location and headquartered in Columbus, Indiana.
  3. Cummins became a leading innovator in engine technology to power a growing industrial economy, and its first direct-injection engine design was the Model F.
  4. By 1928, the company had designed and manufactured the first iteration of today’s diesel engines, built specifically for the commercial trucking market.
  5. Today, Cummins engines are used in medium and heavy-duty trucks and manufactured for commercial engines in many industries and equipment such as construction, mining, drilling, agriculture, rail, and military defense systems.
  6. A Cummins Diesel Engine is an improvement on the original diesel engine technology developed by Rudolf Diesel in 1897, using compressed air to ignite fuel for combustion.
  7. Cummins engines produce greater torque for the rated horsepower, and they have distinct differences in engine block and cylinder head construction, compression ratio, bore, and stroke, as well as firing order.
  8. The Cummins engine has a legendary reputation for being tough, long-lasting, and virtually impossible to kill, originally designed as a commercial-duty engine.
  9. Cummins began to dominate the market for diesel engines in the automotive industry because of its reputation for longevity and durable construction.
  10. Approximately 75% of all RAM 2500 and 3500 Heavy-Duty pickup owners choose the optional Cummins Turbo Diesel, with the 2019 model year offering HD pickup buyers 1000 lb-ft of torque for the first time ever.


In this article, we have covered quite a bit when it comes to the question of what is a Cummins. First, we learned the basics of diesel engines and the pros and cons of running diesel.

Then we covered the Cummins engines. More precisely the 5.9 and the 6.7. These two engines are the most common ones that you will come across if you are on the market for a light-duty truck. We learned their specs and also the common problems that these two engines have.


Now let’s answer some frequently asked questions.

Who Owns Cummins

Cummins is owned by Cummins. They have no parent companies. The main company owns the motor manufacturing process and the nameplate as well.

What Is A Cummins Engine

A Cummins engine is any diesel engine that is manufactured by Cummins. They are the prime manufacturers of diesel motors in the US market along with Duramax and Powerstroke.

What Is A 12 Valve Cummins

A 12 valve refers to the early variants of the B series 5.9 engine. These engines were running two valves per single cylinder and were known simply as the 12 valve engines.

What Is A 24 Valve Cummins

24 valve refers to the improved 5.9 engine in the B-series of engines that included 24 valves. This engine is also known as the ISB engine. This engine basically included double the valves compared to its predecessors and things have stayed this way ever since.

What Is The Oil Capacity Of A 6.7 Cummins

The oil capacity of this engine is 12 quarts, but as many owners claim you only need about 11 quarts on an oil change in order to fill up the engine since some of the oil stays in the engine. So, in order not to overfill it, whenever you replace the oil and filter, after the 11th quart, top off the oil carefully.

How Does A Diesel Engine Work

A diesel engine works differently than gasoline. This engine doesn’t ignite the fuel with the help of a spark plug but by using compression. So, there is no distributor, spark plugs, and other components that are present in gasoline vehicles.

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