The death knell has been ringing for diesel engines over the last decade, primarily because of their environmental impact. But some still swear by diesels for their abundant torque, efficiency, and reliability, with many vehicles racking up miles for years without any issues. They are also a popular choice for farm work, hauling materials, and towing. In fact, about 76% of heavy-duty trucks in the United States run on diesel, compared to around 22% relying on gasoline.
Diesel-powered vehicles generally have a long life, with some cars even surpassing the million-mile mark. For example, one Ford F-350 Super Duty that was featured on the Powerstroke Tech Talk w/ARod YouTube channel ran a whopping 1.3 million miles with its massive 6.7-liter Powerstroke diesel engine under the hood. Nevertheless, like all engines, diesels require regular maintenance and can fail if not properly cared for. With that in mind, here are the mistakes you should avoid if you want your diesel engine to last.
This goes without saying for most vehicles, but it is even more pertinent for diesel cars: never skip your scheduled oil change. Diesel engines operate at higher compression, and they tend to produce more soot and carbonized deposits than gasoline engines. This means that the dirty oil must be replaced periodically to ensure your engine runs smoothly and doesn't overheat — as oil ages, it can cause sludge to form in your engine's internals, reducing its ability to properly lubricate.
Using the right oil is also essential to keep your diesel vehicle running smoothly. Due to the way they operate, diesel engines require specific oils that are formulated differently from those used in gasoline engines. They have additives to help prevent wear, corrosion, and soot build-up, and they are formulated with low-ash content to help safeguard emissions components like the catalytic converter and Diesel Particulate Filter (DPF).
The cooling system in a diesel vehicle has to be running efficiently at all times. Make sure that the coolant is topped up and the system is functioning properly, and follow the manufacturer's recommended interval for a full coolant flush. It's also commonly recommended to check for leaks in the cooling system and replace the hoses as necessary to keep temperatures under control.
An important tip for maintaining your diesel vehicle — simple as it may seem — is to use good-quality diesel. Fuel that's been stored for a long time can accumulate contaminants like dust and water, which can damage injectors and clog fuel filters, as well as the DPF, severely hampering your car's performance.
You also run the risk of having water enter your fuel tank when refueling at poor-quality pumps, as well as from condensation inside the tank. Water is denser than diesel, so it settles at the bottom of the tank, where it can promote microbial growth that may block various filters. The solution is to replace the water separator at regular intervals and refuel your diesel vehicle with high-quality, clean diesel.
A mistake some diesel owners make is running the vehicle with very low fuel, which can have long-term consequences. As mentioned earlier, the bottom of the tank can contain sediment that may get drawn into the fuel system when fuel levels are low, clogging filters and affecting other important fuel system components. Running low on diesel can also cause the high-pressure fuel system to draw in air instead of fuel, which may lead to the engine shutting down until the air is bled out of the system. Diesel is also used to cool the vehicle's fuel pump, so running with very low fuel can reduce cooling and cause the pump to overheat.
Timely replacement or cleaning of filters — such as the air filter, oil filter, and fuel filter — in a diesel vehicle goes a long way toward keeping your engine in top condition. For example, neglecting the air filter can cause long-term issues, as it not only ensures proper airflow for efficient combustion but also restricts dust and debris from entering the engine.
A blocked air filter can make your diesel engine feel sluggish, reduce fuel efficiency, and cause the engine to work harder, especially since diesel engines require a greater volume of air for efficient combustion. Diesel vehicles used in worksites are generally more exposed to dust and debris, so owners should regularly check that their air intake and air filter are clear.
Oil and fuel filters also play an important role in the smooth functioning of any vehicle. Oil filters should be replaced at every oil change, while many experts recommend replacing the fuel filter every 10,000 to 20,000 miles, depending on the vehicle and operating conditions. Ignoring fuel filter maintenance can make the engine run rough and sluggish, and in severe cases allow contaminants to reach the injectors and cause damage.
Modern diesel engines must meet strict emissions regulations, which have led to the development of emission-control systems such as the DPF and EGR (Exhaust Gas Recirculation). These systems reduce the amount of harmful gases released into the atmosphere, but they are prone to carbon buildup, which can reduce performance and efficiency, as well as increase emissions. If not serviced regularly, these systems can also fail and end up burning a huge hole in your pocket.
The EGR system, as the name suggests, recirculates exhaust gases back into the intake to lower combustion temperatures and reduce nitrogen oxide (NOx) emissions. But if the valve becomes clogged with carbon or if the EGR cooler fails, you could be facing a hefty repair bill. To avoid this, periodic cleaning of the intake manifold – either manually or with chemical treatments — can reduce the risk of the valve becoming clogged. It is also recommended to replace the EGR cooler at around the 125,000-mile mark.
The DPF, meanwhile, filters particulate matter from the exhaust gases, but certain conditions can cause it to become blocked, requiring the vehicle to perform a regeneration. If you stop a regeneration midway, the soot that was meant to be burned off can remain in the filter and cause further blockage, which raises exhaust temperatures and, over time, can lead to failures in the turbocharger and other components. In the long run, you could damage the DPF — and this is an extremely expensive component, with Ford's 6.7L Powerstroke V8 DPF costing over $2,000, for example.
While diesel vehicles are versatile and built to be robust enough to handle even the harshest conditions, they still need to be driven with care. They should be driven gently until the engine reaches normal operating temperature, ensuring that the pistons, turbocharger, and other components are properly lubricated.
Diesel engines use glow plugs instead of spark plugs, as found in gasoline vehicles, to heat the air in the combustion chamber. It's recommended to start driving only after the glow-plug indicator on the dashboard turns off, as this signals that the chamber is sufficiently heated for proper combustion. Failing to do so can lead to incomplete combustion, causing unburnt fuel to form carbon deposits inside the cylinders. Warming up the engine becomes even more important in extremely cold conditions, with manufacturers like Ford recommending that owners idle for several minutes before starting a journey.
It's also important to let the engine cool down at the end of a drive so that components — particularly the turbo, which generates significant heat at high speeds — can cool down while oil is still circulating. This is especially vital after spirited driving, hauling a load, or towing. On the topic of towing, diesels are among the best vehicles for the job, but they do have their limits. It goes without saying that you should read your owner's manual and make sure that you never exceed your vehicle's towing capacity.