What Are the Causes of Engine Oil Deterioration?
4 Answers
Engine oil deterioration can be attributed to the following reasons: 1. Filter malfunction: During use, the air filter may wear out or become damaged, allowing external dust to easily enter the crankcase through the cylinder. This increases the viscosity of the engine oil, reducing its lubricating properties. In some cases, it may clog the oil filter, causing the engine to malfunction, leading to damage and shortening its service life. 2. Water ingress into the engine: The most common cause of engine oil deterioration is the presence of water in the oil, which can turn the oil into an emulsion and destroy the oil film. When the water content exceeds 0.1%, the antioxidants and detergents added to the oil become ineffective. If the water content in the oil reaches 1% or more, the lubricating properties of the oil deteriorate, and its viscosity decreases. In severe cases, this can lead to mechanical failures such as engine seizure or bearing damage.
I have deep personal experience with engine oil degradation. After decades of driving, I've observed numerous common causes: prolonged high-temperature operation oxidizes the oil, turning it black and reducing viscosity; extended parking periods lead to natural aging and loss of lubrication; contamination from dust, moisture, or gasoline infiltration worsens during rainy days or traffic jams; mixing different oil brands can trigger chemical reactions; and engine issues like incomplete combustion cause carbon buildup. Prevention is straightforward – change oil regularly every 5,000-8,000 km and never skimp on quality. Last year after a long road trip, my oil thinned noticeably, prompting immediate shop testing to avoid major repairs – a lesson too valuable to ignore.
In the auto repair business, we see a lot, and there are many root causes of oil degradation. High temperatures are the number one killer, especially in summer when engine oil oxidizes rapidly at high RPMs; moisture ingress leading to emulsification is common in short-commute vehicles; fuel dilution issues, such as injector leaks mixing gasoline into the oil; contaminants like metal shavings or dust buildup; oil additive depletion over time failing to maintain the oil film; and mixing oil types, such as mineral with synthetic, accelerates deterioration. I always advise customers to get a full vehicle check every six months and not delay oil changes. If the oil is degraded, replace it immediately—otherwise, engine parts wear out faster, leading to costlier and more complicated repairs.
As an ordinary car owner, I've had issues with my car's engine oil. The reasons include: high temperatures during daily use causing the oil to thicken, which becomes more noticeable after long-distance driving; prolonged use without timely oil changes leading to natural aging and degradation of the oil; contamination such as rainwater seeping in or dust being sucked into the engine; frequent engine start-stop cycles causing excessive water accumulation in the oil; and occasionally using cheap, low-quality oil. Prevention methods: regularly check the oil level and color, and go to the shop for a change if it appears black or has a burnt smell. Last time I delayed changing the oil, it resulted in loud engine noise and cost me over a thousand dollars in repairs—a lesson learned the hard way.
