Owning a diesel vehicle can be a game-changer, offering power, efficiency, and reliability that are hard to beat.
Whether you're a seasoned diesel enthusiast or thinking about switching from petrol, this guide will help you answer common questions about owning a diesel-powered vehicle.
We will start with an overview of common diesel problems and repairs.
Common Diesel Problems & Repairs
When you search for a fault code or symptom related to a common problem with your vehicle on Google, you're likely to find numerous answers—sometimes a hundred or more! So how do you figure out if it is a common fault?
Over more than 30 years working in diesel fuel injection, I’ve seen patterns in what truly causes failures — and what is simply the result of incorrect repairs, poor servicing, or unsuitable modifications.
Fuel System
Common faults within the fuel system are often caused by fuel quality. This is because all diesel fuel systems, common rail and non-common rail, are completely dependent on diesel fuel to hydraulically operate and lubricate the components.
Be mindful of your refuelling point. For example, if you're refuelling from a farm bowser, when was the last time the tank was cleaned or fuel checked? Contaminated fuel is one of the most common causes of major diesel fuel system failure. Fuel contamination can include petrol — If petrol contamination occurs, read our guide on what to do if you put petrol in your diesel.
Injectors
A commonly replaced component in the fuel system is the injector. Often, the failure has been caused by contaminated fuel.
The injectors are part of the same fuel circuit, which includes a fuel pump, rail, and pipes -the image below demonstrates the diesel fuel path in red. In cases of confirmed contamination, workshops may recommend replacing multiple components within the fuel system to prevent repeat failure.
When an injector fails as a result of normal wear and tear, with no signs of contamination, then it is acceptable to replace a full set of injectors. Based on my experience, if the system has done more than 200,000 kilometres, issues can arise afterwards due to the vital matching of the operating system.
Injector Sealing Washers
These provide a secure compression seal between the injector and the seat; it is not uncommon for these to fail.
If compression is lost in a diesel engine, severe consequences will arise. A compression loss will affect the overall performance and eventually fail an engine.
Suction Control Valve
Unfortunately, due to the location of the suction control valves, they have been a common failure. They are part of the high pressure pump and the first valve immediately after the fuel filter.
In vehicles that are poorly serviced or have insufficient filtration, the ultra-fine media paper in the filters can become lodged in the valve. This can lead to it sticking, triggering a fault code, or even causing a loss of power and stalling.
Exhaust Gas Recirculation Valves
The Exhaust Gas Recirculation, usually referred to as EGR. This is the system responsible for reducing harmful emissions.
EGR valves and EGR coolers experience extremely high temperatures whilst removing those emissions from the exhaust. This process causes carbon buildup, causing the EGR valves to stick. If the vehicle is not serviced correctly, these valves may prematurely fail.
Another aspect to consider about the emission system is vehicles equipped with a Diesel Particulate Filter (DPF). Many DPF issues relate to driving patterns, servicing history, or unresolved underlying engine faults — not just the filter itself. We have some helpful tips for maintaining your DPF.
EGR Coolers
EGR coolers are prone to leaking internally. Due to the corrosiveness of the harmful gases recirculated, the cooler can fatigue and begin to leak engine coolant into the system.
Continued coolant loss can eventually lead to serious engine damage if not rectified early.
It is recommended to regularly monitor your coolant tank levels. Mark the coolant reservoir at the upper level when the engine is cold and use this same mark to check the levels at the same temperature.
Turbo Charger
Turbochargers rotate at a high speed, much higher than that of the engine.
We frequently encounter turbo failures in vehicles with poor maintenance records.
In many cases, it has failed early due to driving habits. A turbo requires constant lubrication, particularly because of its high rotational speeds of around 50,000 revolutions per minute (rpm), while the engine would only be working between 800 and 5000 rpm.
The turbo is dependent on lubrication from the engine oil and the oil pump, which is driven by the engine, it is designed to continuously pump oil throughout the engine. The failure of the turbo is caused by the bearings due to a lack of lubrication. The degradation takes place after the engine is switched off, especially if this occurs soon after the engine has been driving at high speeds.
Once the engine is turned off, the turbo continues to spin at approximately 60,000 rpm. Unfortunately, with the engine no longer running, there is insufficient oil supplied to the turbo bearings, which may take longer to slow down, especially if there is no oil present to generate friction. This is why the operator needs to allow the engine to idle for around 30 seconds to 1 minute before shutting the engine off.
Engine Failures
Modifications play a key role in engine failures. Many owners of the modern common rail diesel have never owned a diesel and automatically feel the vehicle does not perform like their previous petrol car. That’s because a diesel suits an entirely different purpose: moving heavy loads with less fuel to do this, not running a ¼-mile drag race.
Other than remapping, fitting a larger exhaust to a diesel has become a novelty, particularly for those who believe it sounds cool and feels like it is performing better. Modern diesel engines are engineered as complete systems. Changing one component without understanding the whole system can reduce long-term reliability. Find out if it’s ok to make your diesel go faster.
Running a larger diameter exhaust may reduce exhaust temperatures, but for a diesel to perform as intended, reducing combustion temperatures can have an adverse effect on the long-term reliability of the diesel engine.
A common modification for diesels is a catch can. Unfortunately, some are fitted for the wrong reason and have contributed to engine failures. Before considering this option, please read what our diesel specialist thinks about Catch Cans.
So, with all these considerations, is it cheaper to service a diesel-powered vehicle?
Happy diesel driving!
Understanding how modern diesel systems operate can help you make informed decisions about servicing, repairs and modifications.
Diesel Help Australia works exclusively with professional workshops.
If you require diagnosis or repair, we can refer you to an independent workshop that is part of the Diesel Help technical support network.
Return to the Diesel Vehicle Owner’s Guide for more topics and maintenance information.
