How Long Do Diesel Engines Last? (Why Do Diesels Last Longer)

When you compare diesel engines to gas ones, you will always be told that the former will outlast the latter. That is not hype but a statement of fact. Diesel motors do last longer than gas engines. There are some good reasons for this gap.

Diesel engines can last anywhere from 500,000 to 1.000,000 miles before needing any major repair work. On the other hand, you would be lucky to get 200,000 miles out of a gas engine. Part of the reason for this disparity is the design of both motors.

To learn more about why diesel engines last longer than gas models, just continue to read our article. It explores the topic so you have the best answer to this question. The longevity is also due to the heavy-duty parts included in the construction.

How Long do Diesel Engines Last?


If the engine is well maintained, it can last a lot longer than 1,000,000 miles. On average you may see these types of engines needing a major overhaul at just over 850,000 miles.

But there is some good news. The major overhaul does not shorten the lifespan of the engine. It will help the engine last up to 1,500,000 to 2,000,000 miles if taken care of.

If we want to put that into hours, as some diesel engines are measured by running hours, that equates to over 35,000 running hours. That total is before the major overhaul is needed.

In terms of years, some diesel engines have been known to last, with proper maintenance, for over 30 years. They outlast the vehicle and its supporting parts by a long shot.

The car or truck that it was placed in was more than rusted out while the engine was still good and could be placed in a better looking vehicle. This is 4 to 5 times longer than a gas engine would last.

One thing is for sure unless it is an exceptional gas engine, it will not outlast the car model in which it is placed. But then the two engines have different designs and different fuels so it is sort of comparing apples to oranges even though the two serve the same purpose.

How Many Miles Can a Diesel Engine Last

We have mentioned this before when we talk about specific engine models. But it needs repeating here as the principle is still the same. The diesel motor option will last as long as its maintenance program.

If there is no maintenance done to the diesel engine, then do not expect to reach even 500,000 miles on it. While a superior motor, the diesel still needs to be taken care of and that means regular oil changes, minor repairs, and so on.

Then given the fact that many modern diesel motors have the DEF emissions system installed, if you want the engine to last, do not put DEF into the diesel fuel tank or diesel fuel into the DEF tank.

This cross fill up is not compatible and either way, you will ruin your engine as well as compile a large repair bill. If you want to get to that 1,000,000-mile mark, then you are going to have to do the maintenance work or have it done regularly by a professional mechanic.

That 1,000,000-mile figure is just the approximate distance you would go until you need a major overhaul. After the overhaul and a good maintenance program, it is not out of the realm of reality to reach another 500,000 to 1,000,000 miles.

The Lifespan Of Diesel Engine


Besides a good regular maintenance program, the longevity of your diesel motor will depend on other factors. One factor will be who made it.

Not every automaker is a diesel engine expert like Cummins. They often try to make their own diesel motor to fit the budget of their customers and to save on costs. Plus, many diesel motors made by Cummins will not fit into a car or smaller vehicle.

The next factor that helps the lifespan of this engine would be the type of parts used to construct the motor. If they are not heavy-duty, then chances are your model won’t last as long as has been already stated earlier.

The quality of the parts will play a significant role. A third factor would be how the engine was driven. If you are hard on motors and push them to their limits, then do not expect a long lifespan. Especially if you do not keep a regular maintenance schedule.

If you own one under ideal conditions, then you can expect the diesel motor to last you around 15 to 20 years before it would need a major overhaul. After that, you may get 5 to 15 more years out of the motor.

But if you are towing heavy trailers all the time, do not expect to get that lifespan out of the engine. Hard work will shorten the life span somewhat.

Do diesel Engines Last Longer Than Gasoline Engines?

Yes, they do. There are some very good and legitimate reasons why this is so. One of those top reasons is that gasoline is a solvent. It is not a lubricant so the parts it comes in contact with will wear down due to the acidic nature of the gas.

This is just a fact of life and very little can be done about this. Then, the thickness of the parts plays a role in the shorter lifespan of the gas engine. Diesel engines are built to last for a very long time, gas engines may receive top-quality components, but the acidic nature of gas will destroy the surface of those parts.

The diesel fuel will lubricate those same parts and has no acidic elements to it. Gas is not lubricating anything but being combusted which will take its toll on the metal parts in a gas engine.

Diesel does not combust as gas does so it is easier on those metal parts. The lack of spark plugs in a diesel engine also contributes to the longevity of the diesel motor. Those explosions in gas engines can take their toll as well.

The diesel does not experience anything like the explosions the spark plugs create. Plus, that is one part a diesel engine does not have to worry about wearing out. A bad spark plug can cause some damage when the gas is not ignited at the right time.

Why do Diesel Engines Last Longer?


First off, diesel engines are made to last forever. With that attitude comes a difference in parts used in this motor over a gas engine. A diesel engine builder uses thicker parts than they would in a gas engine.

There are thicker walls, stronger connecting rods, and other heavy-duty parts that do not wear out as quickly as the same parts on a gas engine. Then, the diesel engine operates at a lower RPM than a gas engine would. Their idle RPM is 750 and their driving RPM is between 1500 and 2000.

The lower RPM creates less heat. That means that the wear and tear on the engine due to heat is less on the diesel engine than on the gas motor. But this is not all the advantages diesel has over a gas motor.

Then diesel engines use more compressed air than a gas engines, 20:1 compared to 10:1 respectively. This difference means that the block, crankshaft, cylinder heads, valves, and pistons are made to endure that difference.

Plus, the diesel engine gets far more lubrication than the gas engine. Where a standard gas engine may use 4 to 5 quarts of oil, many diesel engines require 10. Also, diesel fuel is closer to oil than gas is, so all the parts are lubricated well when you turn the diesel engine on

Finally, most diesel engines are gear driven and not built driven, this gear system makes for more accurate timing. With only a fuel pump and no ignition system, there are fewer parts to break down or wear out.

With fewer parts to break or wear out, the diesel motor will have fewer maintenance needs. Although gas engine makers have been working on that issue for decades. They have developed different components to last longer than they used to.

Are Diesel Engines Reliable?

They are probably the most reliable engine you can ever buy. They are strong, well-built, last a long time, and have fewer parts to go bad on you so they start when you want them to.

The only element you have to be wary about with a diesel engine and starting are the glow plugs. You have to wait till they warm up before you start a diesel engine. If you try starting it too soon, the engine may not start and you will have to wait to start it again.

The modern diesel engines will have warning lights about this and may delay your start a little more until conditions are right for the diesel to get going. Cars and trucks that come with a diesel motor usually have an amber glow plug light on the dash.

When that goes out, the motor is ready to start and should kick over quickly. Just be patient when you own a diesel car or truck. This is not a motor for when you need to rush to your destination because of an emergency or you are late.

You should also not have to do a lot of maintenance to a diesel engine in comparison to a gas one. Diesels are stronger and better built than the gas engines plus, the fuel inside both helps determine the longevity of both motors.

Does Diesel Fuel Last Longer Than Gas?


If you are talking about stocking up on fuel and using it in an emergency or catastrophe, then the answer would be yes, it does. Diesel is made with heavier hydrocarbons which means that they do not break down or evaporate as fast as gas hydrocarbons will.

Then, diesel fuel is less vulnerable to oxidation than gas is. This helps the diesel fuel last longer when you are storing it for a later date. There are two basic types of diesel fuel, ultra-low sulfur diesel (ULSD) and high-sulfur diesel (HSD).

The ULSD can last anywhere between 6 and 12 months if stored correctly. The HSD lasts only have that time frame. What throws a clinker into this debate are the fuel additives used by diesel fuel makers.

Some of those additives will last up to two years so the fuel may last longer than you realize. This time frame is flexible as many factors come into play when you store it.

If you are talking about driving distance and how far you can get on a tank of gas or diesel, then the answer is positive again. It has been proven that diesel fuel is more efficient than gas and will help you travel further.

This too is flexible due to driving habits, road conditions, the weather, and how much weight you are hauling or towing.

Why Are Diesel Engines Better?

They are just built better. The reason they are built better is because of the differences in requirements for each motor. The gas engine does not have to worry about as much compression as the diesel motor does.

That difference means that the diesel engine’s parts have to be thicker, stronger, and able to last for a long time. This is a good thing as you should have less maintenance downtime with the diesel over the gas engine.

Plus, it has been tested and stated that the diesel engine gets 25 to 30% better fuel efficiency than the gas engine. This difference is great for the pocket book. But this is not all the reasons why the diesel is a better engine over the gas.

The fact that the gas is a solvent and diesel is a lubricant plays a large role in the latter’s longevity. The better the lubrication, the longer parts will last. Not to forget that diesel engines are put into some heavy-duty applications that require better components to handle the work.

The heavy-duty parts that are used to build a diesel engine last longer and can handle the power of the engine a lot better. The design of this engine is just better as it has heavier work to do than the gas engine does.

You could say that the diesel is the workhorse engine while the gas engine is the speed and fun motor.

What Makes Diesel Fuel Go Bad


It is a known fact that both gas and diesel will go bad sooner than later. You may have up to a year with ULSD but only if it is stored correctly. Here are some elements that will make the diesel fuel unusable:

1. Light- this can cause a chemical reaction that breaks down the hydrocarbons and make diesel less effective

2. Water & Oxygen- the lower sulfur levels have made diesel fuel more vulnerable to water contamination. When water enters the fuel, microorganisms can grow and clog the fuel delivery system.

Oxygen also degrades the hydrocarbons through a process called oxidation. This will make your diesel fuel less efficient.

3. Extreme heat- if you get into areas where the heat will be up to or over 140 degrees F then your diesel fuel will lose its light fractions and cause deposits to form in your engine.

Comparison Chart

It is hard to put individual engines in a side-by-side comparison as there are always exceptions to the rule. Some people have kept a gas engine going for almost as long as diesel owners have.

The best thing to do is to just compare both engines:

Category Diesel Gas
Lifespan 500,000 to 1,000,000 200,000 approx.
Ignitions system None uses glow plugs that last 100,000 miles Can last up to 50,000 miles
Maintenance Low maintenance Can be high maintenance
Fuel efficiency 25 to 30% better than a gas engine Not as good as a diesel engine
Fuel costs Depends on the market but can be higher than gas Depends on the market and can be higher or lower than diesel
Overhaul costs $9,600 average cost with some motors costing more $2500 to $5000 approx.
Reliable A very reliable engine Reliable but not as well as the diesel engine
Power Better torque lower RPM than a gas engine Higher RPM and lower torque than a diesel engine
Cost Diesel powered vehicles are going to cost more than gas powered vehicles Not as expensive as a diesel powered vehicle

Some Final Words

If you are going to get one car or truck and have it for a very long time, then buy one with a diesel engine under the hood. These motors are superior to the gas options and will last a very long time under the right care.

They are built better and are made to last a lifetime.

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