Problems With Diesel Cars: 6 Common Issues (Explained)

Diesel cars are highly rated in efficiency, durability, and power.

Also, they’re so popular that many of your favorite brands produce diesel vehicles yearly to meet up with the demand. However, just like gas-powered or battery-powered cars, diesel cars have disadvantages.

This article discusses common problems with diesel cars.

Check also our list of the most-common problems with petrol cars.

1. Thickening of Oil

When engine lubricant comes in contact with air, it gets oxidized because it reacts with oxygen.

When this happens, the oil becomes thicker because of the interaction, and this affects its lubricating qualities negatively.

How? You might ask.

Well, lubricants are meant to travel around the engine in specified paths to maintain cooler operating temperatures. It’s more difficult for a thicker liquid to flow through an engine.

Under normal operating conditions, a lubricant would get thicker over time and would need to be changed. However, oxidation speeds up this ‘thickening’ process.

Oil thickening is more common with vehicles that have not been in use for a long period. The air bubbles can lead to friction or even corrosion of engine components.

The presence of this oxidized oil will damage the engine gradually and may even lead to a total breakdown. That’s why it’s best to have it inspected and dealt with on time.

This problem has been reported in several Mercedes-Benz, Volkswagen, and Ford diesel models.

2. Noise in Engine

Generally, diesel engines are louder than gasoline engines because of their mechanical components (which are heavier) and how they operate.

This includes their high compression ratio because they do not use spark plugs to function. Nevertheless, it’s important to note that many ultramodern diesel engines are relatively quiet.

Still, other factors can lead to an even louder noise, which can make them unbearable.

When the noise becomes extreme and abnormal, it may indicate a defect in the fuel injector. This defect can affect the compression balance of the engine, which can lead to further problems.

Diesel-powered trucks usually have the most reports of noisy engines. Some diesel cars with loud noise are the Mercedes-AMG E63 and the Mercedes-Benz Sprinter 3500XD. The Lexus LC doesn’t escape the list either.

This problem can also be unique to Turbo-Diesen engines.

3. Black Exhaust From the Engine

Significant smoke emission is not strange for diesel engines. However, an excessively thick black exhaust emission is alarming.

This excessive smoking usually occurs when air and fuel mix in a poor proportion. There may also be problems with the turbocharger, the EGR valve, the air injector pump, or other engine parts.

Ford vehicles with the Turbo Diesel Common-Rail Injection (TDCi) engine, which uses direct fuel injection, may suffer from this problem. Many complaints have been recorded about thick black smoke from these engines.

Mild smoke is considered normal for diesel engines.

However, when it gets bad, you have no choice but to have it checked and fixed. Legally speaking, you’d be breaking the law if your vehicle is regarded as polluting the environment.

So, if this problem occurs, you should either drive to the mechanic or wait for one to arrive.

You should also know that diesel engine smoke can have other colors, and these colors have different meanings.

For example, blue smoke from the engine translates to excess lubricating oil during combustion. White smoke implies that the temperature in the combustion chamber might be low or that water is seeping in.

4. Low Power

Some causes of low power in diesel vehicles are clogged fuel filters and dirty air filters.

Other reasons include low compression pressure and contaminated oil. Still, the most common reason for low power in a diesel vehicle is a clogged fuel filter.

Fuel filters get clogged over time, and when this happens, it’s difficult for fuel to flow through them. For that reason, the supply to the engine becomes limited and output reduces.

Diesel engines require extremely clean fuel to function optimally because they’re more sensitive to dirt in their fuel system. So, while you can be more liberal with gas engine fuel filters, diesel fuel filters must be strictly monitored.

A problematic fuel pump can also cause low power in cars.

Chevrolet Cruze models are examples of notorious diesel cars with low power and the BMW X5 xDrive 35D is no exception.

5. Overheating Engine

Many factors can cause a diesel vehicle to overheat. Common reasons include coolant leaks, damaged water pump seals, and clogged diesel injectors.

The Ford F-250 and Ram ProMaster are good examples of car models with overheating problems. However, that doesn’t mean you should avoid F-250s entirely.

Usually, a little extra attention and care would suffice so that you don’t have to deal with overheating in any vehicle. This is because most causes of an overheating engine are related to maintenance or early component failure.

So if you own a vehicle with a diesel engine, please always ensure your coolant reservoir seals are not compromised.

A clogged injector adds strain to the engine since fuel supply gets reduced. What really happens is that the engine ‘struggles’ to make do with the little amount of fuel it’s supplied.

As expected, this added strain causes the engine to overheat. If it’s a problem caused by a clogged injector, you can look out for symptoms.

This can also cause start problems for even low-mileage Diesel cars.

A very common symptom is a rough idle that accompanies overheating. Other symptoms include engine misfire and reduced performance. If you notice these symptoms, don’t hesitate to call your mechanic because overheating almost always leads to more problems.

Check our list of problems with old cars.

6. Delayed or Difficulty Start

The two major reasons for a delayed start are low compression and fuel leaks.

Leaking fuel hoses affects the fuel delivery to the engine, and this causes it to stall or lose power. A blockage can also cause fuel delivery issues.

Also, diesel engines ignite combustion by air compression, so they don’t need spark plugs. However, the compression needs a minimum operating pressure, and as you’ve guessed, they can suffer low pressure sometimes.

Cracks on cylinder walls can cause gas to escape and reduce compression pressure.

Unfortunately, in cases of cracks on cylinder walls, not much can be done regarding repairs. Many drivers end up replacing these components. 

As a general rule, maintenance contributes a great deal to the overall lifespan of cars. So after buying a diesel-powered car, paying attention to maintenance might save you from common diesel engine problems.

Related: Will Gas Still Be Available After 2035? (Explained)

General Pros and Cons

Diesel engines are the preferred engine type for large vehicles like trucks and SUVs. This is because they tend to be more suited for heavy-duty tasks. These are some pros and cons of diesel cars:

Pros

  • Impressive fuel efficiency
  • Longer lifespan
  • More torque and power
  • Remarkable relative durability
  • Lower depreciation rate

Cons

  • Higher repair costs
  • More pollution to the environment
  • Louder engine noise
  • Black exhaust from the engine
  • Thickening of oil

Related: 11 Common Problems With Electric Vehicles (Explained)

What Do the Reviews Say?

Edmunds describes diesel vehicles as having “impressive fuel savings over their gas counterparts”. However, they mention their higher purchase prices as being a major disadvantage. So, diesel cars may be fuel efficient, however, they are not usually cost efficient.

It comes down to preference, and how long you intend to use your car. If you use your vehicle for a long period, you may get your money back. Of course, this comes as savings from reduced fuel purchases.

So, if you plan on owning your car for some donkey years, a diesel engine may not be a bad idea for you.

Related: Problems With Used Cars (6 Most-Common Issues)

What Is the Resale Value of Diesel Cars?

Below are the resale values of some diesel cars across various car brands. Note that these are prices specific to certain vehicles, mileage, trims, and locations.

Hence, prices may differ, since your location, model, year, trim, and vehicle condition would be different.

Model Approx. Mileage (Miles) Price ($)
Ford Focus 60, 253 10,265
Audi Q5 34, 201 19,279
Audi Q2 44,360 16,375
Hyundai Tucson 22,154 21,583
Ford Fiesta 32,297 11,066

Despite differences across models, with diesel cars, you have less to worry about concerning resales.

Final Thoughts

Diesel vehicles have been around for a while and they’ve made their mark in the industry. The major selling point of diesel engines is their durability.

However, today, gasoline-powered engines are not their only rivals. Electric and hybrid cars now grace highways, each type with its unique advantage.

Despite the competition, diesel engines still have a ton of benefits and loyal customers. If you decide to buy a diesel-powered car, you can avoid almost any problem with the appropriate care.

Sources

Why Hybrids and Diesels Don’t Always Save You Money | Edmunds

These Diesel Engines Were Nothing But A Massive Disappointment | Hot Cars

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