What Causes Abnormal Noises in Diesel Engines?
4 Answers
Here are the reasons for abnormal noises in diesel engines: 1. The noise is not loud: Many new car owners, after their first maintenance check, may suspect abnormal engine noises when inspecting the car at idle speed with the hood open. If the noise cannot be heard inside the car, it is generally not loud and is usually from the valve area or the fuel injector. The carbon canister solenoid valve can also produce this sound, but it is crisper. One way to distinguish is to slightly rev the engine at idle and see if the frequency changes. If the frequency remains unchanged, it is the solenoid valve; if the frequency changes, it is likely the valve area. 2. The sound is uniform and soft: Generally, during cold starts, the engine noise is slightly louder than when the engine is warm. As long as the sound is uniform, soft, and not harsh, there is usually no problem. This is because, when cold, the gap between the cylinder wall and piston has not yet reached the optimal size, and the oil lubrication is not fully effective. Typically, when the engine block temperature reaches around 95 degrees, the sound returns to normal. 3. Oil-related issues: Poor-quality oil, prolonged lack of oil changes, or low oil levels can increase friction between the valves and guides, as well as in hydraulic lifters, making various engine noises louder. 4. Valve noise: A "ticking" sound after starting the engine is from the valves, especially when the engine is cold. This happens because the oil pressure has not yet built up, and the valve area is not properly lubricated. It usually resolves after a short while. This situation is common if the car has been parked for a long time.
I have experience with diesel engine abnormal noises. Last time my car made a terrifying rattling sound, which turned out to be a clogged fuel injector issue. Actually, common causes mainly fall into several categories: First, fuel injection system failures, such as carbon buildup in injectors, incorrect injection timing, or insufficient fuel supply pressure from the high-pressure fuel pump - these can all make the engine produce metallic knocking sounds. Second, mechanical component wear, like loose crankshaft bearings, excessive piston pin clearance, or damaged valve rocker arms - metal friction from these parts creates harsh screeching noises. Third, turbo system problems - damaged turbine blades produce a sharp whistling sound. Fourth, poor lubrication - insufficient engine oil causes obvious dry friction noise between components. Lastly, loose accessory belts can also cause squealing. When encountering abnormal noises, it's best to first identify the sound characteristics: continuous or intermittent? High-pitched or dull? The most reliable approach is to promptly visit a repair shop for diagnostic equipment checks. Otherwise, minor issues left unattended may lead to major overhauls - that would be a huge loss.
Having driven diesel vehicles for over 20 years, I've encountered numerous strange engine noises. Once during a long-distance trip, I suddenly heard a metallic ticking sound. A mechanic diagnosed it as wear on the connecting rod small-end bearing. Such mechanical wear typically occurs in high-mileage vehicles, becoming most noticeable during hard acceleration. Fuel injection issues are also common - poor fuel quality easily leads to carbon buildup clogging injectors, making cold starts particularly harsh-sounding. Always remember to check the air filter, as restricted airflow can cause abnormal combustion and knocking sounds. If turbocharger blades become deformed, the noise resembles metal scraping and is especially piercing. Belt slippage produces a milder but persistently annoying squealing sound. The key is identifying the noise source - mechanical failures require immediate attention, never risk continued driving. During repairs, always opt for genuine OEM parts, as aftermarket components with larger dimensional tolerances often introduce new abnormal noises.
Recently, my diesel pickup truck also developed abnormal noises, and I've been researching it for a long time. It might be an issue with the fuel injection system, such as clogged injectors or fuel line leaks causing knocking sounds. Mechanical wear like cylinder liner scratches or broken piston rings can produce a ticking noise, often accompanied by a drop in power. Turbocharger abnormal noises are high-frequency whines, with a high likelihood of bearing failure. Insufficient lubrication can cause noise in all rotating components, and a clogged oil filter is particularly dangerous. There are also accessory issues like a loose water pump pulley, which produces relatively mild sounds. Pay special attention to distinguishing: mechanical faults have a metallic quality and rhythm, while combustion issues produce irregular detonations. It's best to use a stethoscope to locate the sound source and avoid disassembling the engine randomly.
