Engine oils are made from a heavier, thicker petroleum hydrocarbon base stock derived from crude oil, with additives to improve certain properties which makes it flow adequately at the lowest temperature and also to minimize the temperature of metal to metal contact between moving parts upon starting up the engine.
The purposes of engine oil is to keep the engine components working smoothly by lubricating them, to protect them against corrosion, absorbed the high temperature from the engine combustion chamber and prevent carbon/sludge from accumulating the engine pan (i.e. bottom tray or sump).
Engine oil is made in different viscosity grades – Single-grades (e.g. SAE 30, 40, 50 e.t.c) which represent the flow of oil when it is warm or Multi-grades (e.g. SAE 5W-30, 10W-40, 15W-40 e.t.c) which changes its viscosity with temperature for better performance of the engine.
It is common knowledge that, vehicle owner should change the engine oil at some point, as required by vehicle manufacturers and engine oil manufacturers. Engine oil changes are usually scheduled based on time in service (i.e. monthly) or the distance the vehicle has covered (i.e. trip or mileage). But the factors that should control when it is appropriate for oil to be change are not usually put into consideration by most vehicle owners.
The factors are as follows;
- How long the engine has run at high temperature either at idle (in traffic) or in motion.
- How many heating cycle the engine has been subjected on a daily, weekly or monthly basis.
- How hard the engine has worked from the last oil change.
Negligence of the aforementioned factors will subject the engine to the following effects;
- It will cause the engine oil & additives to undergo thermal and mechanical degradation.
- It will cause reduces viscosity - which make the oil not capable of lubricating the engine for a longer period of time, increases engine component wear and engine overheat.
- It will cause reserve alkalinity - which make the oil to resist acid formation and makes engine component to corrode.
Some other factors that causes engine oil degradation and its effect;
Combustion by-products - Combustion produces several by-products that also act as contaminants. Water and acids lead to sludge, rust and corrosion. Soot and carbon create sludge and varnish and can clog filters. Unburned fuel in liquid form is deposited on cylinder walls where it leaks past the rings into the crankcase. Sludge deposits collect on oil pump screens, limiting the flow of oil to vital engine parts and resulting in rapid and destructive wear. When oil becomes contaminated its viscosity changes. With soot, dirt, oxidation or sludge, viscosity increases; with fuel dilution it decreases.
Common Contaminants - Dust and dirt from the air enter the engine through faulty air cleaners, some oil fill caps and crankcase ventilation systems. Normal engine wear produces small metal particles that are picked up and circulated by the oil. The abrasive particles of road dust and dirt increase the rate of wear and generate larger metal particles. Those particles are equally abrasive and the rate of wear accelerates with a snowball effect. While filtration removes most of these contaminants, some remain and are left to circulate with the oil.
Extreme Heat - Today's engines are running hotter than ever. More horsepower, turbo chargers and aerodynamic styling have created extremely hot environments that receive less cooling from outside air. High heat leads to oil oxidation, deposits and thickening in conventional oils. Because they are made from impure, irregular molecules, conventional motor oils are more susceptible to the effects of heat. The small, light molecules in conventional oil tend to evaporate as the oil is heated, leaving large, heavy molecules behind and leading to oil consumption and an increase in the oil's viscosity. If those large, heavy molecules are chemically unstable, they may also break-down and form deposits on component surfaces, further inhibiting the release of heat into the oil stream.
Even in relatively mild temperatures, oxygen works to break down some of the chemicals in conventional lubricants. The extreme heat in engines actually promotes oxidation. When conventional oil contaminants break down, they coat components with varnish, deposits and sludge and leave the lubricant thick, hard to pump and with very poor heat transfer ability.
Additional Additives - Careful research and experimentation led lubricant manufacturers to specific chemicals that combat various problems faced by motor oils. These chemical additives are added to base oils as a package. Typical additive packages can include rust and corrosion inhibitors, detergents, dispersants, anti-foaming agents, oxidation inhibitors, extreme pressure additives and viscosity index improvers.
Each additive is designed to aid the base oil in the protection of components, but additional additives have their limitations. While these additives are created to perform specific tasks, they are also subjected to the same extreme environment experienced by the base oil, and each additive is affected by different variables in different ways.
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