What You Should Expect From Diesel Engine Services

May 15, 2022

Although modern diesel-powered cars drive nearly identically to their gasoline counterparts, diesel engine maintenance services differ in many ways due to the mechanical differences between diesel fuel and gas engines.

If you own a diesel passenger vehicle, learn about the tasks that go into full service and the service intervals for each job to keep your engine running smoothly and reliably.

Fundamental Differences Between Diesel and Gasoline Engines

In a typical four-stroke gasoline-powered engine, a cylinder features a piston, a spark plug, a fuel injector, 1-3 inlet ports and valves, and 1-2 exhaust ports and valves. These parts work together to complete the four-stroke cycle, compressing fuel and air into a mixture and using a spark plug to ignite the air-fuel mixture and convert it into energy.

Besides requiring a different type of fuel, a diesel engine has no spark plugs, meaning its four-stroke cycle functions differently. During the intake stroke, only air enters the combustion chamber. When the piston rises, it compresses the air, increasing its temperature.

The fuel injector turns on and sends diesel fuel when the piston reaches its highest position. The air is hot enough for the diesel fuel to ignite immediately and push the piston back down without needing a spark.

A diesel engine typically has better fuel consumption and life expectancy than a gasoline-powered equivalent. However, diesel fuel is more expensive, and a diesel engine repair job is usually costlier due to the increased mechanical complexity.

What Does a Full Diesel Engine Service Include?

Although engines in diesel trucks and cars have a longer average lifespan, they require proper maintenance and regular servicing to function reliably.

If you request full service from competent diesel service technicians, they should inspect your vehicle and offer the following services as needed:

  • Oil change
  • Oil filter replacement
  • Air filter change
  • Urea injection system refill
  • Fuel filter change and fuel system bleeding
  • Draining of the fuel filter water trap

Oil Change in Diesel Cars and Trucks

Unlike modern gasoline vehicles, which can last between 5,000 and 10,000 miles between oil changes (depending on the oil type employed), a diesel motor vehicle requires more frequent oil changes.

Diesel fuel is dirtier and more viscous than gasoline, meaning that your diesel vehicle’s regular maintenance schedule should include oil changes every 3,000 miles or 6 months, whichever comes first.

If you don’t use your vehicle to tow heavy loads frequently, your oil may last up to 5,000 miles or 12 months.

Diesel cars and trucks require different oil than their gas counterparts. Due to the differences between gasoline and diesel engine components, you should only use high-viscosity diesel engine oil. Consult your vehicle owner’s manual to find the right type of oil for your vehicle.

Oil Filter Replacement

Whenever you change the oil in your diesel vehicle, it is also critical to replace the oil filter so your oil can perform at optimal efficiency. Ensure that your diesel service technicians perform an oil filter change after changing the diesel engine oil in your vehicle.

Air Filter Service

Air filters are designed to keep dirt, dust, and other environmental contaminants from entering your combustion chambers through the air inlet, keeping your diesel engine clean. Keep these air filters clean and in good condition to maintain your vehicle’s reliability.

When bringing your vehicle in for full service, your diesel service technicians should inspect your air filter and offer to clean or replace it, depending on its type and current condition. On average, a new clean air filter lasts 15,000 miles before needing a replacement.

One of the most common signs of a dirty or faulty air filter is black smoke from your exhaust. Black exhaust smoke indicates a fuel-air imbalance during the combustion process: your engine does not receive enough air, resulting in partially-burned fuel (and clouds of black smoke).

Refilling the Urea Injection System

As governments enforce increasingly tighter emissions regulations, the automotive industry must adapt and design cleaner and more complex automotive technology to meet these regulations.

One such technology is Selective Catalytic Reduction (SCR). Usually, diesel engines reject a greater quantity of nitrogen oxides (NOx), a harmful pollutant contributing to the formation of acid rain. The SCR system mounts to a diesel vehicle’s exhaust system (much like a catalytic converter), using a particular solution called Diesel Exhaust Fluid (DEF) to catch the NOx from the exhaust gases, reducing NOx emissions by up to 90%.

DEF is also referred to as urea fluid due to its composition (approx. 60% purified water and 40% urea). Consequently, the SCR system is also called the urea injection system. Due to the way this system functions, this system requires periodic refilling.

The mile intervals between urea refills vary depending on your vehicle’s make and model due to the differences in urea fluid tank sizes. A diesel service technician can check your vehicle’s DEF fluid levels and offer a refill if needed.

Fuel Filter Change

A typical diesel car or light-duty truck features a single fuel filter, whereas heavy-duty trucks, farm equipment, and commercial vehicles usually possess two; a primary and a secondary filter.

Although diesel and gasoline vehicles have fuel filters, gasoline is a relatively clean fuel, and gasoline engine fuel filters don’t typically require replacement until well beyond 100,000 miles. In contrast, diesel fuels are dirtier, requiring you to replace diesel fuel filters every 10,000 to 15,000 miles.

Dirty fuel filters are easily recognizable: the filtration elements are typically stained black or dark brown. Common issues and symptoms associated with a dirty fuel filter include decreased engine performance, black smoke leaving the exhaust, increased frequency of engine stalling, and a sputtering sound when driving.

Fuel System Bleeding After a Filter Change

When qualified diesel mechanics fully service your diesel car’s fuel system, they will change your fuel filters, bleed the fuel system, and re-prime it.

Air enters the fuel system during the filter changing process. If air remains inside your fuel system, it will disturb the fuel distribution process (air blocks fuel flow), preventing your engine from starting. For this reason, qualified technicians bleed the system to force the air bubbles out, then prime it again using a primer pump to bring in a new supply of diesel fuel.

Water Trap Draining

One of the most common diesel fuel contaminants is water. Fuel filters are designed to stop water from entering the engine. Because water is heavier than diesel, the filtered water travels downward, pooling into the water trap (also called water separator) at the bottom of the fuel filter assembly.

Some modern diesel-powered vehicles feature sensors and electronic systems that can detect the water levels inside the filter assembly. These electronic systems can also automatically actuate a valve to drain the water.

However, if you have no such system, you’ll need to have the water trap manually drained. Failing to drain the water trap will result in water contamination, in which case your car’s “water in fuel” will light up.

If this happens, bring your vehicle to a diesel engine repair service as soon as possible. If water is allowed to remain inside for too long, it risks introducing corrosion to your engine, severely degrading performance, and potentially requiring multiple thousands of dollars worth of repairs.

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