Your heavy-duty truck is powered by a four-stroke diesel engine system, which enables it to tow and haul heavy loads over thousands of kilometers.

Despite its robustness, the diesel engine is prone to many mechanical problems requiring repair and maintenance.

Therefore, performing a preventive maintenance check is necessary to ensure you diagnose all the components of your vehicle's engine to determine its state and repair and replace damaged and worn-out parts.

Suppose you are a truck operator accustomed to semi-trailers. In that case, you can identify some warning signs of a faulty diesel engine in heavy-duty trucks and report them to the fleet manager or truck owner, who will make arrangements to fix the problem.

Here is a list of some indicators of a defective engine system in your big rig and how you can fix them to ensure its optimum performance and the longevity of your truck.

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Essential Components of a Diesel Engine

Before we examine the indicators of a damaged diesel engine system, it's important to understand the various parts of this engine and how they work to keep them in check and ensure they are well-maintained and up to their functions.

These parts are grouped into seven sub-sections as follows;

• ‍The engine block. It includes the cylinder block, pad, liner, flywheel shell, timing gear, cylinder head, oil pan, and front and rear feet. These parts serve as the skeleton of the diesel engine, supporting and providing room for the installation of other components.‍
• Crankcase and rod mechanisms. They are the moving parts that transfer the mechanical energy from the engine to power different parts of your semi-truck. They include the piston, piston pin and bearing, piston pin spring, crankshaft, piston pin bushing, piston ring, spindle shingle, thrust bearing, flywheel, shock absorber, connecting rod, crank pin and bearing, crank webs, rear oil seal, crankshaft front, and flywheel.‍
• Fuel system. Depending on the engine's needs, these parts store and allow fuel to flow into the combustion chamber. They include a fuel injector, diesel tank, fuel injection pump, filters, and fuel pipeline.‍
• Distribution system. These systems open and close to allow air into the diesel engine and release the exhaust gases. These parts include the camshaft, injector rod, valves, valve spring, lave lifter, silencer, air filter, inlet and outlet pipes, valve door lock block, supercharger, valve seat ring, rocker arm, valve guide, timing gear, and tappet.‍
• Cooling equipment. The system regulates engine temperatures to prevent overheating and knocking. The parts in this classification are the fan, water tank, thermostat, water pump, water pipe, thermostat, fan belt, and water filter, among others.‍
• Electrical systems. These systems are responsible for powering, lighting, and monitoring various truck operations. They include the alternator, battery, starter solenoid, start motor, relay, circuit, and switch.‍
• Lubricating system: It comprises an oil sump, oil filter, oil drain plug, oil pump, oil pipes, sump filter, and pressure-regulating valves. These help reduce friction in the engine's moving parts to prevent wear and tear.

How a Semi-Truck Diesel Engine Works

The diesel engine operates effectively using four strokes: exhaust, compression, intake, and power.

When you press the brake pedal and turn on the ignition key, the starter motor cranks the engine, rotating the crankshaft. This movement causes the pistons to move up and down, compressing the air inside the cylinder.

Continuous air compression increases the temperature of the air inside the cylinder. When the air has attained the required temperature, the fuel injectors release diesel into the hot air, igniting and producing mechanical energy.

This process continues, producing enough mechanical energy to power the engine and distribute power to the other parts of the truck through relays, fuses, and circuits.

Important note; The diesel engine uses compressed air to ignite the diesel as opposed to petrol engines that use park plugins to ignite the petrol.

11 Common Warning Signs of a Damaged Diesel Engine in Your 18-Wheeler

After you've understood the different parts of the diesel engine and how it powers your 18-wheeler, let's look at some signs of a defective diesel engine and how you can fix them to ensure your semi-truck operates safely, keeping your driver and other road users safe.

1. High Fuel Consumption

As a diesel truck driver or fleet manager, you know the distance your 18-wheeler will cover with a tank full of diesel before the low-fuel light turns on. 

If your engine has problems, your truck will consume more fuel than usual to produce the same power needed when accelerating or hauling heavy loads. Diesel leaks, incomplete combustion, or a defective engine will lead to poor fuel economy and higher fuel costs.

Sometimes, you may notice that your truck is consuming more fuel than usual, this is a sign that your engine has problems. An experienced diesel mechanic will diagnose your engine to identify and fix the problem.

2. Unusual Black, White, or Blue Smoke From the Exhaust System

Your semi-trailer can release black smoke due to incomplete combustion brought about by clogged air filters and fuel injectors, malfunctioning turbochargers, or faulty injectors. It indicates an imbalance between the fuel-air ratio in the combustion chamber, and some diesel may fail to burn, producing thick black sooth.

If you notice some blue smoke escaping from your vehicle's exhaust system, this is an indicator that oil is present in the combustion chamber. Oil can only enter the combustion chamber if the PCV malfunctions or the valve seals and piston rings wear out.

If white smoke with a sweet smell escapes from your truck's exhaust pipes, it indicates that coolant has entered the combustion chamber. Your cylinder head, head gasket, or engine block may be faulty. Sometimes, the white smoke can result from incomplete combustion caused by worn-out or clogged fuel injectors.  

3. Your Engine is Overheating

Modern trucks have temperature sensors to notify you when your diesel engine is overheating. Leaks in the coolant system cause your vehicle to lose fluid, lowering its level and thus preventing the engine from cooling as required.

Moreover, if the thermostats, radiators, or cooling fans are faulty, they may fail to cool the engine as required, causing it to overheat. If you notice your engine overheating, you can pull your truck off the roadside and allow the engine to cool or visit a nearby diesel truck repair shop to have the issue fixed.

4. Fluid Drops Below the Truck

When you notice liquid stains below the truck, it is a sign that your vehicle has leaks. These stains can result from oil, coolant, or transmission fluid leaks from your semi-trailer. 

If the leaks are not fixed on time, the oil, coolant, or transmission fluid levels will reduce, and your engine will corrode due to friction and overheat, reducing its ability to work efficiently. 

On the other hand, you may frequently add the oil, transmission fluid, and coolant as you notice an unusual drop in their levels. Contact a professional diesel mechanic to inspect and fix the issue.

5. The Presence of a Strong Smell When the Engine is Running

Faulty fuel injectors or a malfunctioning turbocharger will lead to incomplete combustion. As a result, some diesel may fail to burn and escape into the environment with other exhaust emissions. The unburnt diesel escaping through the exhaust will produce a pungent smell. 

If you notice some unusual diesel smell when your engine is running, ensure you reach out to your diesel mechanic to diagnose your truck, trace the problem, and fix it.

6. Strange Noise Originating From Your Semi-Truck's Engine

You can tell if your diesel engine has a problem if you hear loud knocking, grinding, or banging noises from the engine section. These noises result from damaged connecting rods, engine gears, piston slap, or bearings.

Conversely, if your engine produces a hissing or whistling sound, it can indicate that your air intake and exhaust systems have leaks.

7. The Check Engine Light Turns on

The onboard diagnosis system detects engine problems in your truck and relays the message by triggering the check engine light on your dashboard. 

Do not ignore that sign to prevent the problem from escalating. Ensure you have your diesel engine checked and any issues repaired before they cause any further costly damages.

8. Your Vehicle Fails to Start 

Sometimes, you may press the brake pedal and turn on the ignition key, expecting your engine to start, but it fails. You may experience this during a cold session or average weather when your truck engine sleeps for hours without operating. 

Your semi-trailer may fail to start because of a drained or worn-out battery, a faulty starter motor, a clogged fuel injection system, a glow plug, and a malfunctioning turbocharger. 

If your truck's battery is drained, you can jumpstart it using jump starter chambers with another vehicle whose battery is functioning. Then, you can allow your semi-truck to run for about 10 minutes for the battery to charge before you drive it.

Also, remember to seek help from a nearby truck repair shop to repair and replace the damaged components to ensure your vehicle remains operational and keeps your driver and other road users safe.

9. Your Diesel Engine Keeps Running After Turning Off the Ignition Key

You switch off the ignition key to cut the fuel supply to the engine and power off your truck, but instead, your diesel engine won't shut down but keeps running. 

Probably, your engine is running because of the damaged piston and rings that will allow oil to leak and enter the combustion chamber. In addition, a malfunctioning turbocharger will keep running and force diesel into the combustion chamber to keep the engine running.

10. Excessive Vibrations

Excessive shaking or vibrations may occur when accelerating or at rest while the engine runs. This is another sign of a lousy diesel engine and should be addressed immediately.

11. Power Loss

A damaged engine will lose power, causing abnormal acceleration. Sometimes, the engine may shut down while the vehicle is on the road, requiring towing to the repair shop.

Once you realize the vehicle is not increasing its speed when you try to accelerate, this issue can be related to your engine. Sometimes, your truck's fuel filters, fuel pump, turbocharger, or exhaust system may be at fault.

Contact your diesel mechanic to inspect your truck and ensure the issue is fixed. If not addressed, it can lead to costly repairs and even put the lives of the driver, passengers, and other road users at risk.

Need Help With Cleaning, Repairing, or Replacing Your Truck Engine?

If you need help cleaning your diesel engine, diagnosing and repairing it, or replacing the whole engine or a damaged part, our professional and experienced Truckup mechanics will do it right.

Whether you need mobile mechanics to attend to your truck on the roadside or at your private parking lot, our experienced mechanics are ready to help. Contact the mobile mechanics in your area to have your issue fixed.

Conclusion

Once you notice any of the signs we have discussed, do not hesitate. Ensure you get a qualified diesel truck mechanic to diagnose your truck, identify the real culprit behind your engine misbehaving, and fix it to prevent accidents and avoid costly repairs.

As a fleet manager or truck owner, you can advise drivers to spot and report any issues. This helps with preventive maintenance and keeps your semi-truck running smoothly.

Frequently Asked Questions (FAQs)

1. How Do I Know if My Diesel Engine is Bad?

You can tell if your diesel engine has a problem if you notice the following signs: black, blue, or white smoke from the exhaust system, excessive shaking or vibration when accelerating or when your truck is resting as the engine is running, a strong smell of diesel, your vehicle fails to shut down after switching it off, your engine takes long to power on or fails to start, your 18-wheeler is consuming a lot of fuel, your semi-trailer is overheating, or your truck takes time to accelerate or fails to accelerate.

2. Can I Drive My Truck With a Defective Diesel Engine?

The Federal Motor Carrier Safety Administration(FMCSA) restricts truck drivers or owners from operating trucks with issues. A faulty engine can put the lives of your driver, passengers, and other road users at risk. Ensure you have it fixed and tested to confirm it's safe before it starts operating.

3. Can Bad Fuel Cause Engine Failure?

Contaminated or poor-quality fuel can corrupt the combustion process, damage the internal combustion engines, make your engine misfire, clog the fuel pump, or even corrode the sensitive parts of your diesel engine, damaging it. Ensure you use the correct fuel type to keep your engine healthy and prolong its lifespan.

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