Motor oil performs several functions within an engine. It lubricates, creating a protective film between moving components to minimize friction and wear. It aids in cooling by carrying heat away from hot parts, supplementing the primary cooling system. The oil also works to keep the engine clean by suspending contaminants and preventing deposit formation. Additionally, it helps seal the gap between piston rings and cylinder walls and protects against corrosion of internal engine components.
Core Degradation Processes
Motor oil undergoes chemical and physical changes over time, leading to breakdown and reduced effectiveness.
Oxidation
Oxidation occurs when oil molecules react with oxygen. High temperatures within an engine accelerate this reaction, forming acidic compounds, sludge, and varnish. As oxidation progresses, the oil thickens and loses its ability to flow properly, impairing lubrication. Antioxidant additives delay this process, but their effectiveness diminishes.
Thermal Breakdown
Thermal breakdown involves the oil’s molecular structure breaking down due to extreme heat. When oil is subjected to temperatures above 400°F (204°C), its molecules chemically change, leading to viscosity loss and carbon deposits. This process reduces the oil’s ability to protect engine parts, causing increased friction and wear. High temperatures can also accelerate oxidation, creating a cycle of degradation.
Mechanical Forces
Mechanical forces within the engine contribute to oil degradation through shear stress. Multigrade oils contain long polymer chains called viscosity modifiers, which help the oil maintain its thickness across a range of temperatures. However, constant squeezing and rubbing between moving engine parts, such as in bearings or between gear teeth, can physically break these polymer chains. This permanent shearing causes the oil to lose viscosity, making it thinner and less protective.
External Contaminants and Their Impact
Beyond the oil’s intrinsic degradation, various external contaminants can enter the engine’s lubrication system, impacting oil performance and longevity.
Fuel Dilution
Fuel dilution occurs when unburnt fuel seeps past piston rings and mixes with motor oil. This dilutes the oil, reducing its viscosity and compromising lubrication.
Water and Moisture
Water and moisture can contaminate motor oil, often from condensation or coolant leaks. Water contamination promotes rust and sludge, which can clog oil passages and reduce lubrication. It can also form acids that corrode engine components.
Dirt and Debris
Dirt and debris are abrasive contaminants. These particles circulate with the oil, acting like sandpaper to accelerate wear on engine parts. They can also contribute to sludge and deposits, hindering oil flow and heat transfer.
Combustion Byproducts
Combustion byproducts, such as soot and acids, are another source of contamination. Soot can cause the oil to thicken and form sludge. Acids, formed from combustion gases, can corrode engine metals.
Coolant Leaks
Coolant leaks introduce antifreeze into the oil. When antifreeze mixes with motor oil, it forms a thick, sticky sludge that clogs oil passages and filters. This contamination can lead to inadequate lubrication and engine damage if not addressed.
Consequences of Degraded Oil
When motor oil degrades, its ability to protect the engine diminishes, leading to several negative outcomes.
Reduced Lubrication
Reduced lubrication is a key concern, as thinned or contaminated oil fails to create a protective film between moving parts. This results in increased metal-on-metal friction and accelerated wear on components.
Sludge and Deposits
Degraded oil leads to the formation of sludge and deposits. Oxidation byproducts and suspended contaminants coalesce into residues that coat internal engine surfaces and clog oil passages. Such blockages restrict oil flow, starving engine parts of lubrication and hindering engine operation.
Corrosion and Rust
Acidic byproducts from oxidation and combustion, along with water contamination, promote corrosion and rust. These corrosive elements attack engine components, leading to surface damage and weakening parts. This compromises engine integrity.
Overheating
Overheating can occur as oil degrades because it loses its capacity to transfer heat away from engine components. Increased friction from poor lubrication also generates more heat, exacerbating the problem. An engine running hotter can suffer further oil degradation and component failure. Ultimately, these combined effects can lead to serious engine problems, often resulting in costly repairs or engine failure.
Maintaining Oil Integrity
Regular oil changes are a key practice for preventing motor oil breakdown and preserving engine health. Adhering to manufacturer’s recommended oil change intervals ensures fresh oil, with its additives, is circulated. This removes contaminants and replenishes protective properties.
Using the Correct Oil
Using the correct type and viscosity of motor oil is important. Engines are designed for specific oil formulations that provide optimal lubrication and protection. Employing the wrong oil type can lead to insufficient film strength or inability to withstand engine conditions, accelerating degradation.
Checking Oil Level
Regularly checking the oil level is a simple maintenance step. Maintaining the proper oil level ensures engine components receive adequate lubrication and the oil system can dissipate heat. Low oil levels can lead to heat buildup and accelerated oil breakdown.
Addressing Leaks
Addressing any leaks promptly prevents external contaminants from entering the lubrication system. Leaks can introduce substances that compromise oil quality. Timely repairs safeguard oil integrity and engine cleanliness.
Driving Habits
Driving habits influence the rate of oil degradation. Severe driving conditions place greater stress on motor oil. These conditions can accelerate oil breakdown and may necessitate more frequent oil changes than recommended for normal driving.