4 Common Issues In Diesel Engines And How To Address Them

Most people prefer diesel engines because they’re more durable and fuel-efficient than gasoline engines. But just because they’re stronger doesn’t mean they don’t encounter various engine problems. 

If your engine isn’t maintained frequently, minor issues that could easily be fixed or prevented can worsen and cost more in the future. A diesel engine that’s unable to start is an example of a minor issue. To resolve this issue, you need to check the fuel pump, fuel supply, fuel lines, and fuel filters. Clogged filters could be the cause, so you’ll have to replace them. Another factor could be dirty air filters, which should be cleaned regularly or replaced if needed.

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Hence, regular maintenance is necessary to keep your diesel engine running well for a long time. Make sure that the engine remains clean. Inspect the engine fluids and change the air, oil, and fuel filters frequently. In case you’re in search of diesel engine parts for replacement, you might want to have a peek here or check out other online sources.

While regular wear and tear is typical for any engine, there are common issues that diesel engines face. Continue reading to learn more about these issues and how to address them. 

1. Engine Overheating

Overheating occurs when an engine is pushed beyond its limit, thus causing damage to the crankshaft and bearings. Pistons expand and scrap against the cylinder wall, and cylinder heads swell, distort, and break. Moreover, engine overheating can occur when the cooling fan is damaged. Blocked diesel injectors, broken thermostats, faulty radiator hoses, and coolant leaks are also common causes of engine overheating.

What you can do to deal with this problem is to first identify the root cause. Have an experienced mechanic inspect it. If the cooling fan is the cause, an easy solution is replacing the faulty fan with a functional one. If the diesel injectors are causing the problem, have the mechanic replace them. If the bearings, crankshafts, and pistons are damaged by overheating, let the mechanic replace them too. But if the problem is due to a coolant leak, seal the leaks and refill and replace the coolants.  

2. Black Exhaust 

Unlike in the old days, diesel engines are efficient and don’t emit as much black exhaust as they used to. Black exhaust isn’t exactly a problem but rather an indication of other issues in your engine. It can be a sign that your fuel and air mixture is out of balance. Diesel engines require a mixture of fuel and air to run, so if your air filters are dirty and are preventing enough air from combustion, you’ll notice black exhaust. 

Additionally, over-fueling can cause black exhaust. It occurs when the fuel injector wears and erodes the injector needle, thereby allowing excess fuel into the combustion chamber. Carbon build-up causes black emissions as well, especially in old engines.

Like addressing overheating, you must figure out the root cause of black emissions. A general solution is to examine, replace, and clean air filters. Cleaning them will allow enough air into the engine for complete combustion. 

Aside from cleaning filters, you need to clean or replace your fuel injectors regularly, so there will be enough fuel in the combustion chamber. Old engines with carbon build-up use high-quality diesel additives to help clear the build-up.

3. Oil Oxidation

As mentioned earlier, a diesel engine requires air to start and run. It also needs air in the combustion chamber. If your oil system leaks, air can penetrate the motor oil, causing the oil to oxidize. 

Oil oxidation occurs when oxygen reacts with oil, leading to a permanent chemical change. It can result in issues, such as sludge and deposit formation that decrease the engine’s efficiency and cause engine failure and additive depletion, which reduce the oil’s effectiveness. Furthermore, it produces increased oil viscosity, decreasing oil efficiency and degradation, so you’ll have to change the oil immediately.

Although the oxidized oil isn’t dirty, its chemistry is destroyed. Therefore, it should be changed to prevent further issues. In addition to changing them, you can use synthetic base oils and oxidation inhibitor additives to slow the oxidation process. The base oils work by preventing oxygen from attaching.

4. Contaminated Fuel 

Diesel is more viscous than other fuels, meaning it’s easily contaminated. Common contaminants include water, dilution, glycol, mold, bacteria, and soot. When these contaminants enter the fuel injector, they can cause significant issues and engine disruption. For instance, fuel contamination leads to low engine power, black exhaust, poor fuel economy, and frequent filter replacement. In a worst-case scenario, it can keep your engine from running.  

To handle or prevent the issue, you can remove water from the fuel tank if water is the contaminant. Since water is denser than fuel, it settles at the bottom, so you can remove it by opening a valve at the lowest part of the tank. Use a diesel fuel contamination test to check for contaminants. If the fuel is contaminated, drain it and replace it with uncontaminated fuel.


Though tough, durable, and fuel-efficient, diesel engines also encounter issues. However, conducting regular inspection and maintenance of your diesel engine will prevent and address issues effectively. If you notice there’s an issue in your engine, consult a certified mechanic as soon as you can.

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