Diesel engines use gas and compressed air without the need of an additional component like a spark plug for combustion. Because of its different design from the ubiquitous spark-ignition engine, it can also experience different problems. Common diesel engine problems include diesel runaway, bad glow plugs causing starting issues, and black smoke. This list covers the top 5 problems diesel engine owners can experience.
Top 5 Problems with Diesel Engines
1. Diesel Runaway
Symptoms of Diesel Runaway
- Engine revs extremely high
- Engine won’t turn off after putting the key in the off position
Causes of Diesel Runaway
When a diesel engine is running out of control at a high RPM, it’s a sign that diesel runaway will occur. If there is a mechanical failure or another type of failure like an engine oil or fluid leak, it can cause diesel runway (i.e. the engine not turning off and running on its own). Over time, the RPMs will continue to rise, which will also be an issue.
Diesel engines are not meant to run at high RPMs but low RPMs. The valves above the pistons have compressions springs that can mechanically fail at higher RPMs and can stick open or shut, causing the piston to run up and down, which can seize and damage the engine.
What to Do If Diesel Runaway Occurs
Steps to Take for Diesel Runaway
- Pull Over and Park
If the problem starts to onset, pull over and park.
- Put a Manual Transmission into 4th or 6th Gear
With a manual transmission, put your foot on the brake and put it into 4th gear or 6th gear depending on the gas in the system.
- Release the Clutch Quickly to Stall the Engine Out
Release the clutch quickly. Hopefully that will stall out the engine.
- Block the Engine from Pulling in Air
Pop the hood. Block any air the engine is trying to pull in. Go to the air filter area and disconnect the air intake tube or open the air in the box. An ABC dry chemical fire extinguisher can smother out any oxygen that the engine could breathe. If it can’t breathe, it can’t run.
- Open the Decompression Valve
Some vehicles have a decompression valve you can twist open which effectively will turn it off. Without compression, the engine can’t run.
- Diagnose the Cause
With the engine off, let it cool and continue diagnosing parts like the valves to prevent diesel runaway in the future.
2. Engine Lubrication Issues
Symptoms of Engine Lubrication Problems
- Difficulty starting the engine is the most common symptom
Causes of Engine Lubrication Problems on Diesel Engines
Improper oil viscosity can allow air into the hydraulic system, which could affect the fuel injection unit. If the fuel injection unit is not getting the right amount of pressure, it will not release the right amount of fuel.
How to Prevent Engine Lubrication Problems
Check the owner’s manual and use the manufacturer’s recommended oil.
3. Glow Plugs Failing
Symptoms of Bad Glow Plugs
- Difficulty starting or turning over the engine
Causes of Bad Glow Plugs
Glow plugs are a wear item and they tend to fail. Diesel engines use glow plugs to heat up the air prior to starting the engine. If there is not enough heat, the engine will have difficulty turning over. It will feel like it doesn’t want to turn over, or it will turn over very slowly.
Once the engine is started, the glow plugs turn off until the engine is started again. They have a heater element inside of them that can break down over time, which weakens the voltage in the electrical current.
How to Fix Bad Glow Plugs
If you’re having starting issues, have the glow plugs inspected. If the glow plugs are in bad condition, replace them.
4. Black Exhaust Smoke
Symptoms of Black Smoke on Diesel Engines
- Big billow of black smoke of out of the exhaust
Causes of Black Smoke
Black smoke is one of the common problems diesel engine owners can experience. It is caused by improper fuel-to-air ratio inside the engine, which means the engine is likely running too rich (i.e. the engine is running with excessive fuel).
5. Fuel Injection Pump Failure
Symptoms of a Bad Diesel Fuel Injection Pump
- Engine shaking, misfiring, or not running properly
- Slower acceleration than normal
- Smoking exhaust
- Issues cranking or starting the engine
How to Fix a Diesel Fuel Injection Pump
Diagnose what caused the fuel injection pump to fail since another part is usually involved in its failure.
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