What Causes Excessive Negative Pressure in the Engine Crankcase?
2 Answers
The reasons for excessive negative pressure in the engine crankcase are as follows: Poor piston sealing: This leads to air leakage, allowing the air-fuel mixture to escape into the crankcase, increasing the gas volume and pressure inside the crankcase. Blow-by gases: During engine operation, high-pressure combustible air-fuel mixture and burned gases from the combustion chamber may leak into the crankcase through the gap between the piston assembly and the cylinder, causing blow-by gases. Engine oil deterioration: Blow-by gases consist of unburned fuel vapor, water vapor, and exhaust gases, which dilute the engine oil, reduce its performance, and accelerate its oxidation and deterioration. Component wear: Moisture condensation in the engine oil forms sludge, blocking oil passages. Acidic gases from the exhaust mix into the lubrication system, causing corrosion and accelerated wear of engine components. Blow-by gases also increase crankcase pressure excessively, damaging the crankcase seals and leading to oil leakage.
I have been engaged in automotive repair for over 20 years. Excessive negative pressure in the engine crankcase is usually caused by internal sealing issues. The most common reason is worn or poorly sealed piston rings, which allow high-pressure gases from the combustion chamber to leak into the crankcase, creating excessive negative pressure. Another common cause is a malfunctioning crankcase ventilation system, such as a clogged or stuck PCV valve, or carbon buildup in the ventilation pipes, obstructing normal airflow. This can lead to a series of chain reactions, such as oil emulsification, increased oil leaks, and even heightened engine vibration. When encountering such issues, I recommend that car owners first check if the PCV valve is clean and replace or clean the pipes if necessary. Don’t forget to change the oil and filters regularly, as this can significantly reduce wear. If neglected for a long time, it can result in reduced power, skyrocketing fuel consumption, and even damage to the engine’s core components, so early detection and treatment are crucial.
