Common Diesel Engine Problems and How to Fix Them

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( — July 22, 2020) — You may never experience any issues with your diesel engine. But then, when it happens, you want to get back on the road as fast as possible. Being able to identify some of the problems that diesel engines encounter will help with that. There are various reasons why your diesel engine is acting unusual. While it’s frustrating to have it not working entirely, it’s better to check your engine, and see if you have any of these common problems before the issue worsens or you experience total engine failure.

Engine oil issues

Your car runs for thousands of miles. Therefore, it’s subject to wear and tear. The most common problem linked to engine issues is engine oil. This is the lubricant that reduces wear on moving parts. When your car or truck sits around for too long without moving or remains in storage between seasons, then expect problems with the oil oxidizing. 

Oil oxidation means that air gets into the oil and creates bubbles that disrupt proper lubrication, resulting in a faltering or even a damaged engine. The oil may not be technically dirty, but it still needs to be changed after staying idle for too long.

The use of improper engine oil will also create problems like hard starting and engine failure. If you use the wrong oil, it will allow air into the hydraulic system that helps the fuel injection pump, creating a foam that results in fake fuel injection pressure. It’s essential to use the correct engine oil that manufacturers recommend for different seasons of the year, as well due to humidity changes and other weather-related issues. You may use single weight oil during summer, while multi-weight oil will suffice to ensure proper engine function in winter.

Engine oil contamination can also cause problems in your engine. Common oil contaminants include diesel fuel, water, or coolant. Coolant or fuel in the oil will cause low engine oil pressure, leading to engine stuttering or engine failure. Excess fluids in the oil will cause high oil levels in the crankcase. High oil levels generally point to fluid leakages somewhere else in the engine. 

Your mechanic will determine where the leak is coming from and make necessary repairs. After that, the oil should be drained and refilled with the approved grade diesel engine oil. It’s also advisable to change your oil filters. Sometimes, the low oil pressure is due to something as simple as clogged filters.

Smoke from the exhaust

Black smoke

When you notice black smoke coming out of your exhaust, there’s a problem. Black smoke means an imbalance in the air to fuel ratio, too much fuel to lacking enough air. This may be due to these reasons- there’s too much fuel being added to the pump, or there’s not enough oxygen being supplied to burn fuel. The black smoke is usually full of large diesel particulates that should have burned as fuel. When your car is emitting black smoke, then it means that the engine isn’t getting the optimal fuel mileage it deserves.

The most common causes of black smoke include faulty injector pump, faulty injectors, bad air filter (which is creating lack of enough oxygen supply), and a bad EGR valve (which may cause the valves to clog up), or even a faulty turbocharger. A good mechanic can fix all these and maybe they could also replace your exhaust by using MBRP exhaust systems.

White smoke

White smoke coming off your exhaust means that the fuel injected into the combustion chamber isn’t being burned correctly. The common lead to white smoke includes water in the fuel pump, low engine compression, or the fuel pump timing thrown off. This is because an obstruction prevents the fuel from getting into the pump in the way necessary for the pump to have proper timing and work efficiently.

If the white smoke is thin like vapor and disappears after the car warms up, then there’s no serious issue because the vapor is just steam due to condensation from a cold morning. If the smoke is thick white, then it’s either faulty injector timing or water in the fuel tank, and in this, you’ll need to get it fixed at the repair shop.

Blue smoke

Blue smoke will be emitted if your engine is burning engine oil. This is usually a mechanical problem because if engine oil leaks into areas where it can be burned, then the result is a thick blue smoke emitted from your exhaust. The problem may be a faulty injector pump, which causes the oil to mix with fuel and be burned. Another reason for oil mixing with fuel is that the valves or the valves’ stem may be faulty. Worn out cylinders and piston rings are another reason they let the oil flow where it shouldn’t. The other simple reason is putting too much oil in the engine where it overflows and mixes with fuel, causing it to burn. Simple fixes can correct all these problems at the repair shop.

Faulty diesel fuel injectors

The fuel injection system is the heart of your diesel engine. The system is essential for pressuring and injecting fuel into the air compressed in the combustion chamber. It feeds fuel into the injectors, adjusts fuel quantity and timing, and also atomizes the fuel.

The fuel injectors help improve fuel efficiency, reduce the need for fuel system maintenance, and keep emissions cleaner. The average lifespan of your diesel fuel injector pump is around 100,000 miles. A typical injector consists of the injector body and the nozzles. If any of these two get clogged or faulty, then it compromises the entire vehicle performance. If you suspect any of the following signs with your diesel car, then your injectors are faulty.

  • If you’re having issues igniting your car or experiencing uneven idling, and also, if the engine cranks but doesn’t start unless you crank it for a long time, it’s a warning sign your injectors are faulty.
  • If the car is misfiring, and if your car is misfiring when you ignite, a complete diagnosis will involve finding the combustion process that’s lacking. There could be lack of proper fuel injection or the fuel charge in one of the cylinders failed to ignite, and therefore, no combustion.  
  • Fuel odor. The smell of diesel inside the cabin could mean that you have a leak somewhere. This means that you have a terrible injector that allows the diesel to flow out of the nozzle.
  • Dirty emissions. Injector deposits and clogged fuel filters will cause incomplete and uneven fuel combustion, resulting in thick smoke emissions from your exhaust. 
  • Low fuel economy. Faulty injectors will burn more fuel, which will lead to increased fuel combustion and impact your vehicle’s efficiency and performance. 

If you’re experiencing or suspect any of the above problems, you either need to clean your fuel injection pump or get a new one from who are professionals in diesel engine parts. 

Defective glow plugs

A glow plug’s purpose in your diesel engine is to preheat and help warm up the engine cylinders, so that the fuel combustion can occur efficiently. They play a vital role in warming the engine cylinders during cold starts, where starting the engine is usually tricky. When you have failing or bad glow plugs, they can cause problems with the vehicle’s performance and eventually lead to engine failure. Glow plugs use an electrode that warms up and glows orange when current is applied. Here are some issues you may experience with your vehicle if you have faulty glow plugs.

  • Engine’s misfire or decrease in power acceleration. When your engine misfires, it’s usually the first warning sign that you have an issue with your glow plugs. If the glow plugs are faulty, they won’t provide the additional heat that helps in diesel combustion, which causes engine misfires. Engine misfires may result in a loss in power, fuel efficiency, and acceleration.
  • Hard starting. Unlike gasoline engines, which generally use a spark to ignite the fuel, diesel engines usually rely on cylinder pressures to ignite the fuel. If the glow plugs don’t work, the engine will have to overcome more pressure to ignite the fuel, resulting in hard starting. 
  • Smoke from the exhaust. Defective glow plugs may obstruct the combustion process, which may cause the engine to release smoke.  

Glow plugs are found on all diesel engines and play a crucial role in igniting and operating the engine. If your diesel engine or car shows any of the issues above or you suspect you have failing glow plugs, have the vehicle inspected by professionals.


The list above doesn’t comprise all the things that could be wrong with your diesel engine and causing you problems. It’s just meant to give you an idea of what could be going on under the hood. If you have further questions or severe problems with your diesel engine, it would be best to contact your mechanic.