Diesel engines are known to last up to five times longer than gasoline engines. In the recent past, however, they have had a bad rep for the effect they have on the environment.
This has affected sales, with some brands such as Porsche and Toyota choosing not to make them anymore. The good news is that not all diesel engines contribute to pollution.
Some car manufacturers have found ways to reduce the amount of toxic emissions they produce. This, coupled with their ability to last longer than gasoline engines, has helped improve their reputation.
In fact, diesel engines easily clock 1,000,000–1,500,000 miles on the odometer and can keep going for as long as 30 years. Most petrol engines last just about 200,000 miles.
In this guide, we’ll take a look at some of the reasons why diesel engines last so long. Let’s dive in.
Why do diesel engines last longer than gasoline engines?
- Engine design
- Better lubrication
- Fewer parts
- Diesel characteristics
- Lower RPMs
- Engine application
1. Engine Design
Diesel engines have thicker walls, larger pistons, bigger blocks, and a tougher build. They are bulkier than gasoline engines and comprise several heavy-duty components that are resistant to wear.
This is due to compression ignition. Unlike gasoline or petrol engines, diesel engines do not use spark plugs to ignite fuel. Fuel is injected into charged compressed air inside the combustion chamber to cause an explosion.
Compression ignition is ideal because diesel is less volatile and has less self-ignition tendencies. Petrol, on the other hand, burns easily and is more volatile. If you light a match and drop it in a puddle of gasoline, it will light ablaze almost instantaneously.
Diesel isn’t as flammable. Air must be compressed first to make it combustible before diesel is introduced. The compression causes a considerable amount of heat and pressure inside the cylinders.
It also happens quicker than spark ignition. To make sure the engine can handle the pressure, car manufacturers ensure that the components are tough enough. Larger pistons cover a larger internal volume in the cylinders to provide enough capacity to ignite the fuel.
The larger crankshaft and camshaft are also fitted with larger bearings and stronger main and rod bolts. The valve train is more durable and includes harder and more solid rollers. This makes the engine durable in the long run and allows it to last longer than a gasoline engine.
2. Better Lubrication
Diesel engines have a larger capacity for oil thanks to their larger crankshaft, camshaft, bearings, and cylinder heads. They provide more room for oil. A diesel engine can use as much as 15 gallons of oil compared to 1 gallon in gasoline engines.
Cooling jets are installed to spray oil at the bottom of the pistons. The oil prevents premature wear by reducing friction. It also cools the bearings by absorbing the generated heat. All moving parts ride on a thin film of oil.
Diesel engines also feature a higher capacity for cooling. This significantly reduces overheating. Multiple thermostats and sensors are installed to monitor the temperature of the engine. They ensure that a constant stream of coolant flows through the piston cooling nozzles.
If any of the sensors fails, the others take over to keep an eye on the engine. This keeps the motor operating within the right temperature range. The coolant flows to the cylinder liners, heads, and other engine components while absorbing heat.
3. Fewer Parts
Many diesel engines do not use a timing belt or chains to synchronize the rotation of the camshaft and crankshaft. They are gear-driven. This means that you do not have to worry about stretching, squealing, cracking, and other defects that come with serpentine belts.
The gears are fixed and hardly ever lose their timing. This also means that there are less chances of having problems with the oil pump and water pump. If the gears fail at any point, they can be repaired quickly without losing timing.
It’s good to note that some diesel cars use a belt to drive the cam and valves, such as those fitted with the VW TDI diesel.
Many diesel engines also feature flat tappet camshafts with flat bottom valve lifters rather than hydraulic lifters. This means that there are no hydraulic lifter problems to worry about. They also lack spark plugs which are used in gasoline engines to ignite fuel and air.
The use of compression ignition eliminates the need for spark plugs. Diesel doesn’t ignite so there is no need for them. The fuel has a high flash point, which is the temperature at which it can form an ignitable mix with air.
Another part that lacks in most diesel engines is a distributor cap. This is a device that directs high voltage from the ignition coil to the spark plugs. Having fewer parts means that there are fewer components that can break down easily. They won’t have to be repaired or changed often.
4. Diesel As a Fuel
Diesel has lubricating properties that allow it to lubricate parts of the engine as it flows within the cylinders. It takes the form of a light oil that helps to reduce friction between moving parts.
On the other hand, gasoline is more of a solvent. It tends to be more acidic and can be a poor lubricant. The high temperatures inside the engine can alter the blends of gasoline and ethanol and cause corrosion in metal.
The petrol will then eat away at the cylinder rings. Diesel engines are also said to be more fuel efficient. They give up to 1.5 times the fuel efficiency of gasoline.
The amount of chemical energy converted into mechanical energy by a diesel engine is far greater. The fuel is denser than petrol and contains roughly 15% more energy by volume.
5. Lower RPMs
Another reason why diesel engines last longer than gasoline engines is because they work less to produce the same amount of power. A gasoline engine will achieve about 2500-3500 RPMs while a diesel engine will do 1300-1600 RPMs.
This means that the former is doing double the work. This causes a significant increase in the amount of wear and tear inside the engine. It also generates more heat, which tends to account for about 75% of the wear in many engines.
6. Engine Application
Diesel engines are commonly found in trucks and vehicles designed for high mileage. This is because they go long distances without powering down. It’s not uncommon for semi trucks to cover as much as 300 miles in a single day.
This allows the engine to achieve maximum operating temperature. The diesel particulate filters (DPFs) also get hot enough to burn harmful emissions. Overall, it improves the performance and efficiency of the engine.
On the other hand, gasoline engines found in passenger vehicles only get to cover about 10 miles or less per trip. They also experience frequent starts and stops that do not allow the engine to get to its optimum operating temperature.
These actions can strain the engine as it tries to match the driving demands. Diesel engines are able to maintain the right temperature range throughout the day with shorter temperature cycles. This allows them to last longer than gasoline engines.
Even though diesel engines survive longer than petrol engines, they require proper maintenance and servicing at the recommended intervals. They boast superior construction and can cost more in repairs compared to their counterparts.
For this reason, it’s important to take good care of your engine. Also, it wouldn’t be fair not to mention that modern gasoline engines are catching up in terms of durability. Many have been known to last as long as 500,000 miles.
No matter the type of engine, proper care and maintenance cannot be neglected. It is the number one determinant of whether your engine will last longer than the average motor. Change your fluids as recommended and replace any damaged parts.
Related Questions on Diesel Engines
How many miles can a diesel engine last?
Diesel engines can last up to 1.5 million miles before needing a repair overhaul or engine swap. This means that you can drive your diesel car for more than 30 years without ever having to replace the engine.
Is 100k miles a lot for a diesel car?
If you’re out in the market for a car, avoid anything with more than 100,000 miles on the odometer. Used cars that have been driven that much will cost you time and money in repairs. You’re better getting a diesel engine with fewer miles.
What are the disadvantages of diesel?
In countries where fuel isn’t subsidized, diesel tends to cost more than gasoline. Diesel cars are also more expensive than petrol cars due to the higher cost of making the engine. Other costs that are higher include insurance premiums and repairs.
Will short journeys damage diesel engines?
Short journeys can cause damage to the diesel particulate filter (DPF). This is a device that reduces the amount of pollutants that a diesel vehicle produces. The exhaust needs to get hot enough for it to burn the harmful pollutants. This often requires long journeys.
Is it bad to cold start a diesel?
Experts recommend not using diesel cars as often in areas with sub-zero temperatures. The fuel turns into jelly as certain hydrocarbons start to turn gelatinous below 400F. However, most of today’s cars are built to start in cold weather with little effort.