The Beauty of Diesel Engine Maintenance

I think it’s safe to say that much of the soul of the American hot rodder is still alive in diesel culture. Where late-model muscle cars have refined and smaller work trucks lean toward comfort, diesel engines stand strong and continue dumping raw, unadulterated power on the table. With any engine, more power means things are more likely to break. And while diesels are incredible rigid, and don’t share many of the same weak points typical of gas engines, they still have certain sensitivities.

Here are some areas to pay extra attention to when practicing routine diesel engine maintenance.

Fuel Water Separator

We all know that water in any fuel system is an issue. Diesel fuel is highly hygroscopic, which means it will pull a lot of moisture from the air. A fuel water separator is used to pull this water from the fuel, so it can be drained later during routine diesel engine maintenance. A sensor will usually alert you when this needs to occur, but some people time theirs to their oil changes. This is something you will need to get a feel for based on your own experience, but is definitely something you don’t want to overlook.

If ignored, the water can damage fuel injectors, affecting engine efficiency and potentially even causing engine failure.

You Def Need DEF Fluid

Speaking of alien fluids, an important part of diesel engine maintenance is adding diesel exhaust fluid. DEF is used as a catalyst to reduce harmful NOX emissions given off by the engine. Modern diesel trucks are designed to take the DEF very seriously. In fact, if the tank runs too low on particular models, the computer will actually stop the truck from performing normally by reducing its top speed down to 5 mph until the DEF tank is refilled.

According to free education service, discoverDEF.com, “Medium and heavy-duty vehicles have a dosing rate of 2-3%. This means that if your truck has a fuel efficiency of six miles per gallon and a dosing rate of 3% it will use approximately 1 gallon of DEF every 200 miles. Feedback from a number of fleets suggest that the dosing rate is slightly lower than originally predicted by manufacturers, at around 2.0-2.5%.”

This DEF consumption calculator can help you determine your appropriate annual and monthly DEF usage.

Fuel Filters

A great way to tell how different diesel engines are from gas engines is how sensitive the fuel systems are. With gas engines you obviously need to be mindful of your fuel filters, but in diesel engines a clean fuel filter is critical to proper performance. Some gasoline engines may only need a fuel filter change every 30,000 miles or so. With diesel engines, however, it’s recommended to replace the fuel filter every 10,000-25,000 miles, depending on your vehicle and commute. (And be mindful that fuel injectors need to be changed every 50,000-100,000 miles.)

“Failure to replace both your primary and secondary fuel filters at the recommended interval can cause them to become contaminated with either debris or chemicals that can plug the filters, resulting in decreased fuel flow and a loss of fuel pressure,” says Ford Motor Company. “This can ultimately cause damage to the fuel injectors.”

This is especially important to be mindful of in the cold weather, as any water that may still be in the fuel—even with a separator—can freeze up in the filter hindering fuel flow. To learn more about wintertime diesel engine maintenance, click here.

Keep it Cool

Another thing diesel engine owners need to be mindful of is the quality of their coolant. Ford 6.7 Power Stroke owners, in particular, need to pay special attention to this area to make sure the nitrite levels in the coolant are within proper range. To test this, you’ll need specialty strips to dip into the coolant to get an accurate reading.

This is critical to keep an eye on, as it works to protect the cylinder sleeves from cavitation. This is a leading cause for engine failure, as cavitation on the sleeves reduces the structural integrity of the cylinder. If the coolant’s nitrite levels are low or the coolant quality is poor it should be replaced immediately.

Clean Air Filters

Diesel engines are just as sensitive to air quality as they are to fuel quality, making cleaning and replacing the air filter an important part of diesel engine maintenance. This means checking the quality of the air filter as frequently as possible.

Now, it’s going to vary from environment to environment but take this into consideration: diesel engines react very well to air intake system modifications and the same is true for contaminants. A clogged filter can definitely lead to reduced fuel efficiency and power in considerable amounts.

“Diesels create higher compression ratios and require tighter tolerances,” explains K&N Filters. “That’s why we build diesel air filters to even higher specifications. They typically use deeper pleats in larger sizes to increase surface area for more capacity and airflow … [and] contain more cotton in different grades and configurations to achieve higher levels of efficiency.”

Keep Your Eye on Oil Levels

Let’s close on one last, important concept: diesel engines are going to burn oil. Now, those of us on the gasoline side of the spectrum are no strangers to this, either. There are many gas engines known for burning oil like crazy, but generally speaking, that’s usually a sign of a worn engine or dated design. With diesel engines, though, it’s something of a natural phenomenon.

“New developments in diesel engines have led to lower emissions in heavy-duty vehicles. These new technologies can make as much as 30% higher torque—but they also bring higher engine temperatures and pressures,” explains Castrol. “This can lead to accelerated oxidation and oil thickening, increased build-up of deposits, and rapid depletion of the oil’s acid-controlling reserves. All of this can push the oil closer to breakdown and reduce useful oil life.”

That means, regularly popping the hood and ensuring oil levels are within a safe range of oil capacity needs to be a part of your regular diesel engine maintenance. As we all know, the worst thing you can do to an engine—no matter how tough it is—is run it out of oil.

Sure, routine maintenance of any kind can feel like a chore. But when it comes to securing your investment—an investment that brings some serious power and efficiency to the table—it’s a fair trade off.