Under what circumstances does an engine require a major overhaul?
4 Answers
An engine requires a major overhaul under the following circumstances: 1. When there is excessive clearance between the piston and cylinder wall causing blue smoke emission, a major overhaul is necessary. 2. Severe black smoke emission from the engine. If cylinder pressure measured with a compression gauge is below normal values, a major overhaul is required. 3. Abnormal noises during engine operation. When unusual sounds are detected, the engine must be disassembled for inspection or measured using an engine noise detector. 4. Knocking sounds from connecting rod bearings (big end and small end bearings), especially when the small end bearings are severely burnt and the crankshaft shows significant wear. 5. Scuffing sounds from cylinder walls. Upon disassembly, severe scoring is found between pistons and cylinder walls.
I've been driving a taxi for over a decade, so I know exactly when an engine needs major maintenance. Generally, after hitting 80,000 kilometers, it's time for a major service – think of it as a middle-aged health check. The spark plugs should be replaced by then; the original ones have served their purpose. The oil filter and fuel filter must be completely renewed, like giving the car fresh blood. The timing belt needs thorough inspection – if it snaps on the highway, the engine is done for. The throttle body is surely caked with thick sludge and needs a deep clean. Finally, check for carbon buildup in the cylinders with a borescope to see if the piston tops are black. This full service can add years to your car's life, far better than breaking down midway.
Last time after off-roading, the engine light came on, and the technician said it was a classic sign for a major service. Constant low-speed off-roading is most likely to cause carbon buildup in the engine, with noticeably slower throttle response and a muffled popping sound during acceleration. In addition to the usual oil and three-filter change, it's essential to focus on cleaning the intake tract and fuel injectors. Also, long-term rough driving can easily cause the engine mount bushings to wear out, leading to increased vehicle vibration. My Land Cruiser had all its engine mounts replaced during service, and the vibrations disappeared immediately. For friends who enjoy road trips, it's recommended to perform a major service every 50,000 km or two years, especially for vehicles frequently driven on rough roads.
It's time to consider a major maintenance service after driving a new car for five or six years. Don't wait until problems arise, as repairs will be more expensive then. I just had my sedan serviced last month, mainly replacing all fluids: transmission fluid, coolant, brake fluid - these all deteriorate over time. I upgraded to iridium spark plugs, and fuel consumption immediately dropped by 0.5 liters. The technician also used walnut shell blasting to clean carbon deposits from the combustion chambers, and now cold starts are exceptionally smooth. They paid special attention to inspecting the timing chain, which fortunately hadn't stretched. I recommend replacing various bushings at the same time, as rubber components will age and crack over time.
