What Causes Engine Oil to Leak Out?
5 Answers
Engine oil leaking out is caused by the aging of the four supporting components, cylinder liner, piston, piston rings, and turbocharger. Reasons for the aging of the four supporting components: Failure of the "three filters" allows dust and impurities to enter the cylinder, causing abrasive wear. After replacing the four supporting components, the engine was not properly run-in according to the technical requirements, leading to excessive carbon deposits when the engine does not burn fuel completely. These deposits fall off and cause abrasive wear. Reasons for the aging of piston rings: Light leakage in piston rings, insufficient elasticity of the rings, reverse taper in rings with outer taper due to production issues, poor thermal stability of the rings, and significant loss of elasticity.
I've encountered the issue of engine oil leaking out several times, and there are two most common causes. First, aging or cracked seals or gaskets, such as the valve cover gasket or oil pan gasket, shrink and crack under prolonged high temperatures, causing oil to seep out. Second, excessive crankcase pressure—when the PCV valve fails, internal pressure rises too quickly, forcing oil out. Another possibility is overfilling the oil; if too much is added, it can overflow due to thermal expansion. I recommend you stop the car immediately and check for oil stains on the ground, then feel the hood temperature to see if it's abnormal. If too much oil leaks, it could pollute the environment at best or cause engine overheating or even fire at worst—definitely not worth the risk. Quickly find a reliable repair shop to replace the worn-out parts before it escalates into a major overhaul. During regular maintenance, pay attention to the oil level and keep it around the middle of the dipstick marks.
That day I had just finished a long drive and noticed oil stains under the engine, which gave me a scare. Oil leaking out could be due to seal failure, such as a loose oil pan screw or worn cylinder gasket, causing oil to be squeezed out. Additionally, if the oil type is unsuitable or low-quality oil is used, it can easily corrode the seals. Another common factor is severe piston ring wear, allowing compressed gas to enter the crankcase, increasing pressure and causing oil overflow. I must remind you to check the oil dipstick level yourself—if it exceeds the upper limit, it's an overfilling issue. Also, look for oil stains near the air filter, which is a sign of a clogged PCV system. Timely action is crucial; otherwise, if all the oil leaks out, the engine will be ruined. It's recommended to have the technician check the gasket lifespan during oil changes and ensure maintenance every 5,000 kilometers.
From a mechanical perspective, oil leakage is mostly caused by component wear or failure. Worn piston rings allow combustion chamber gases to enter the crankcase, increasing pressure and forcing oil out. Failed valve guide seals are another common cause, allowing oil to seep through gaps. Additionally, a clogged crankcase ventilation system that prevents pressure release, or a rusted-through oil pan can lead to leaks. These issues frequently occur in older vehicles, so regular engine condition inspections are recommended. Simply put, you can observe the oil's color and smell – if it's blackened or has a burnt odor, it indicates severe internal wear. Preventive measures include using high-quality oil and avoiding high-load driving. If oil leakage is detected, stop the vehicle immediately to prevent damage to core components.
When you notice oil seepage, don't take it lightly as it poses a significant threat to driving safety. The main factors include cracked oil pan gaskets, overfilling engine oil beyond the maximum limit, or malfunctioning crankcase ventilation valves causing pressure imbalance. Engine overheating also exacerbates oil leaks due to expansion, potentially leading to fires. I recommend first turning off the engine to check oil levels and look for leakage traces, commonly found beneath the engine. Also inspect around spark plugs for possible cylinder gasket leaks allowing oil passage. Routine maintenance shouldn't overlook oil quality and change intervals - six-monthly inspections can prevent issues. Severe leaks may ignite the engine, making prompt repair the best course. Maintain good driving habits; reducing sudden acceleration lowers risks.
