Diesel engines are the pinnacle of automotive engineering. The first diesel engine was invented by Rudolph Diesel. Back then the engines were large and cumbersome and did not produce much power. But over the years with modern engineering methods and ideas, diesel engines improved and became the powerhouses that we know them as today.

Modern-day diesel engines can run to as much as 1,000,000 to 1,500,000 miles. That’s about ten times the life of a gasoline engine. But why is that so? Well, there are several reasons but we will look at the most important ones below.

The Remarkable Diesel Engine Design

Why are diesel engines more reliable?

The real reason diesel engines are reliable is that they are designed to be that way. Diesel engines are fundamentally different from gasoline engines. At first, you will notice that size is the biggest difference. Diesel engines have a larger combustion chamber compared to gasoline engines.

The camshaft and crankshaft along with the pistons are all bigger. This also results in better oil clearance allowing the lubricant to move freely within the block. Lubrication naturally decreases wear and tear of crucial parts in the engine. Perhaps, this is the biggest win for the diesel engine. Furthermore, the average gasoline engine can drink up to 4 liters/gallons of oil while a diesel engine consumes considerably more.

Moreover, diesel engines function with the help of gears. There are fewer moving parts, which means reliability is not an issue. You will find no timing belts but rather gears that run every major function. The gears are fixed and move smoothly making the whole operation a breeze.

A diesel engine will also use oil pumps to create pressure and help the engine function. These engines are also better in terms of heat dissipation. Multiple thermostats and heat sensors adorn the engine allowing the engine to work constantly without facing overheating issues. Plus, the radiator and the coolant do their job to the max.

We mentioned that diesel engines are bulky, that is because they are built with high-quality components. A diesel engine block has to sustain more pressure as compared to a gasoline engine block. There is rarely any work done to reduce the weight of the engine.

In other words, the bulkier the engine the better it is at supporting high-torque. The camshaft, the valves, and other vital engine components are also heavy duty. Diesel engines are heavily tested according to the highest industry standards whereas gasoline engines are not tested very frequently.

Diesel vs Gas

The second most important factor is fuel. Diesel fuel is less volatile and less reactive than gasoline. It burns slower and does not go to waste. Gasoline fuel on the other hand is highly volatile and it ignites with even the smallest of sparks. This often leads to misfiring and eventually to the damage of cylinder heads.

Furthermore, gasoline acts as a poor lubricant, since it quickly burns away it does not assist the combustion chamber. Diesel fuel is a bit thick and consistent and its slow-burning nature allows it to lubricate the combustion chamber with ease. It is only through highly compressed hot air that diesel fuel ignites and even then it takes time to reach full combustion.

RPM Differences

rev counter

The RPM capability of an engine plays an integral part in its reliability. This is why we do not see high rpm motors in road cars, since engines that can handle such RPMs are expensive to build and they are highly unreliable.

Take an example of F1 cars that can reach up to 18000 RPM but those engines last for only a few races before breaking down entirely. Therefore, most street-legal family sedans and SUVs limit their RPM range to 6500 RPM.

The diesel engine wins in this regard. It does not rev very high and it produces double the amount of turning force or torque for half the RPM of a gasoline engine. For example, a diesel engine will produce the same amount of power at 1500 RPM that a gasoline engine will produce at approximately 3000 RPM. So, in other words, the gasoline engine works harder to make the same amount of power. All of this results in extra wear and tear for the engine. The diesel engine simply wins in this regard by being less susceptible to wear and tear.

Lower RPM in diesel engines also allows more torque to go through to the tires resulting in better performance in low RPM ranges. This is why they are highly popular in off-road vehicles like SUVs and pickup trucks. Moreover, a diesel engine is like a marathon runner. It can function continuously for 200 to 300 miles without needing a break. Gasoline engines, on the other hand, need to be cooled down and given some rest before they can start working at full capacity.

Diesel engines also have a very low RPM limit. Some will even max out at 5000 RPM but the initial burst of energy they provide is second to none. You can witness that power in monster trucks that perform stunts and excrete thick clouds of black smoke, all of that at low RPMs.

No Need for Regular Maintenance

mechanic checking diesel engine

Since diesel engines have less moving parts and less wear and tear they do not need to be overhauled that often. Gasoline engines require regular maintenance such as an oil change (equally important in a diesel engine), spark plug change, timing belt adjustment, and more stuff. Diesel engines do not have spark plugs therefore they don’t need to be opened very soon.

You will see diesel engines being redone after thousands of miles and even when they are not performing optimally they provide enough performance that you will not feel the need to visit the mechanic. Your diesel car will produce a lot of black smoke, however, which is not a good sign for the environment.


Keeping in mind the reasons discussed above it is clear why the diesel engine last considerably longer than gasoline engines. The aforementioned factors allow the diesel engine to last more than 1,000,000 miles. When compare that figure to the average lifespan of a gasoline engine, which is 100,000 miles, you will feel nothing more than shock. Just a slight difference in design and functionality makes such a huge difference in performance, reliability, and longevity.

No matter how much you try to be careful with a gasoline engine it will not be able to return the favor in terms of higher total mileage. A poorly kept diesel engine will also give you multiple times better mileage than a well-kept gasoline engine.

Sadly, even though diesel engines have a lot of benefits they are quickly phasing out of the automotive world. The biggest issue with such engines is pollution and that is the biggest enemy for climate change. Countries like Germany and Europe as a whole has imposed restrictions on diesel-powered vehicles and created a timeline for their phasing out process.

Soon, the power and might of diesel engines will be replaced by electric-powered vehicles who deliver the same amount of power if not better than diesel engines. This is perhaps the last generation of people that will see mass-produced diesel vehicles in action before they are written-off as part of automotive history.