What Are the Common Engine Faults and Their Causes?
2 Answers
Eight common engine faults and their causes: 1. Engine cold start shaking: The engine shakes during cold start idle but returns to normal after warming up. The main reason is excessive carbon deposits inside the engine. During cold starts, the fuel injected by the injectors is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture, making it difficult to start. Only after the carbon deposits are saturated with fuel does the engine start easily. Once started, the fuel adsorbed on the carbon deposits is reabsorbed into the combustion chamber, enriching the mixture. The fluctuating air-fuel mixture causes idle shaking after a cold start. Another cause could be faults in spark plugs or ignition coils. 2. Engine hot idle shaking: The engine shakes during hot idle. There are many causes for this, the most common being engine misfire. Generally, check the spark plugs, ignition coils, fuel injectors and fuel system, exhaust blockages, fuel grade compatibility, carbon deposits in the engine, carbon buildup in the throttle body, and the firmness of engine mounts. 3. Engine abnormal noise: Engine noises can be categorized into cold and hot engine noises. Cold engine noise: Often caused by oil draining back into the oil pan after prolonged parking, preventing the oil pump from establishing oil pressure and forming an oil film immediately during a cold start, leading to inadequate lubrication and noise. Hot engine noise is usually more serious and harder to diagnose, often due to piston slap or knocking. Crankcase ventilation leaks can also cause loud noises, and the car belt may produce noise at certain speeds, usually due to slippage or aging. 4. Engine carbon deposits: Carbon deposits form mainly from incomplete combustion during engine operation, along with gummy substances produced by impurities in fuel and oil, accumulating over time. 5. Dirty throttle body: The main cause of carbon buildup in the throttle body is the reciprocating airflow during engine intake and exhaust strokes. Not only does it draw in air during intake, but gas reflux during valve overlap can also lead to carbon deposits. Additionally, the crankcase forced ventilation in front of the throttle body reintroduces exhaust gases into the combustion chamber via the intake valve, directly causing the throttle body to become dirty. 6. Engine oil burning: The causes of oil burning are varied, ranging from manufacturer specifications to component damage. Some vehicles burn oil almost as much as they consume fuel. Excluding manufacturer issues, new cars rarely burn oil (after the break-in period). Common causes include incorrect oil grade, aging or damaged valve seals, piston ring sealing issues leading to oil blow-by, damaged crankcase ventilation or oil separator, and cooling/lubrication issues in the turbocharger. 7. Engine oil leaks: There are many causes of oil leaks, most commonly due to aging gaskets. Common leak points include aging or damaged oil pan gaskets or loose bolts, loose drain plugs, missing gaskets, damaged threads, aging timing cover gaskets, leaking valve cover gaskets, front and rear crankshaft seal leaks, aging oil cooler gaskets, and leaking oil filter housing gaskets. 8. High engine coolant temperature: High coolant temperature is indicated by temperature warnings or boiling over. Common causes include faulty thermostats disrupting the cooling cycle, dirty radiators reducing efficiency, insufficient coolant, trapped air in the cooling system, faulty electric fans, water pump failures, or faulty temperature sensors.
When it comes to engine failures, I've seen quite a few as an auto technician. Starting difficulties are the most common, usually caused by a dead battery or a faulty starter motor. Rough idling often results from spark plug carbon buildup or ignition coil failure. Engine noises may come from belt aging or crankshaft wear. Overheating is a frequent issue, typically due to radiator blockage or coolant pump failure. Power loss can stem from clogged fuel injectors or intake system problems. Routine maintenance is crucial – checking fluids and replacing parts can prevent most issues. Oil leaks are another headache, usually caused by aging seals and gaskets. Addressing problems promptly is key to preserving engine lifespan. I always advise car owners to perform monthly self-checks on oil levels and coolant temperature gauges to avoid major repairs. Never delay fixing minor issues – early small repairs lead to longer vehicle longevity.
