What's in Motor Oil
Your car's oil has two primary ingredients: base oil and additives. The base oil lubricates the engine's moving parts to reduce the friction that causes wear. The additives prevent the engine's heat from breaking down the oil.
Base Oil
The base oil is refined from crude oil pumped from the ground. The crude is refined to remove undesirable components such as wax, sulfur and nitrogen compounds and to extract or remove unsaturated hydrocarbons. These processes are part of the refinement:
Solvent extraction separates the naturally occurring saturated and unsaturated hydrocarbons.
Hydrofinishing removes some of the nitrogen and sulfur compounds, and improves color, oxidation and thermal stability of base stock.
Hydrotreating converts some of the unsaturated hydrocarbons to saturated hydrocarbons to help improve yield. This process also helps remove a lot of sulfur and some nitrogen compounds.
Hydrocracking is a sophisticated process in which molecules are rearranged into the desirable saturated hydrocarbon molecules. The yield of saturated molecules is much greater than achieved with hydrotreating and solvent extraction.
Hydroisomerization, when used with hydrocracking, can transform the molecules of the base stock into the most stable form possible.
Additives
Base oil alone is not enough to properly protect your engine. A motor oil needs to perform a wide variety of functions under a wide range of engine operating conditions. Therefore several additives are incorporated into the formulation:
Detergent/dispersant additives keep the engine clean, suspend the various contaminants in a fine suspension and preventing them from settling out on vital engine components.
Rust and corrosion inhibitors protect the engine from water and acids that are byproducts of combustion.
Antioxidants inhibit oxidation process, which can make the oil thicken and sludge form.
Anti-wear additives form a film on metal surfaces to prevent metal-to-metal contact.
Viscosity modifiers and pour point depressants make motor oil flow better.
Oil Grades and Viscosity
Oil thins when heated and thickens when cooled. For motor oil to keep lubricating your engine throughout the seasons, choosing the proper grade of viscosity for the ambient temperature in your region becomes vitally important.
A monograde oil's viscosity is for only one temperature, either cold or hot or low. A multigrade must meet both high and low temperature viscosity requirements simultaneously. Multigrades are an easy and popular year-round choice for drivers who experience hot summers and harsh winters. You can recognize them by the dual viscosity designation (10W-30 where the 10W is the low temperature and the 30 is the high temperature). The viscosity modifiers thicken the oil at high temperatures but are inactive at low temperatures.
You can find information about the performance, viscosity grade and energy-conserving properties of an oil in the American Petroleum Institute (API) Service Symbol, also known as the "doughnut." This symbol displays the API service rating, a two-letter classification that identifies the quality level of the motor oil and the type of vehicle it's suited for.
- If the first letter is S, the oil is appropriate for "spark ignition" or gasoline engines. A C means the oil is for "compression ignition" or diesel engines.
- The second indicates the performance level of category. For the S categories, the performance level increases through the alphabet. The same isn't true for the "C" categories as the types and intended application range for diesel vehicles vary greatly. It's important to refer to the owners' manual for appropriate performance recommendation.
In the center of the doughnut is the Society of Automotive Engineers (SAE) viscosity classification. The bottom of the doughnut conveys the energy-conserving properties of the oil as determined in a standard industry test.
If an oil meets both the latest S service category and the current energy conserving standard, it's allowed to display the API Certification Symbol, known as the Starburst, on the front label.
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