Motor Oil - The Basics
Motor Oil - The Basics
OK, we've established that it's important for you to change your oil religiously. It's vital for your car's engine to have clean, fresh oil to properly do its job. But you still may be wondering what motor oil is exactly and how it works.
Well, let's start with the basics. The oil used in your car has two primary ingredients: base oil and additives. The base oil allows the motor oil to perform its vital function - lubricating the engine's moving parts to protect them against wear and tear caused by friction. The additives provide additional engine protection by helping prevent the oil from deteriorating under the extreme temperature conditions in the engine.
The base oil is refined from crude (oil in its natural state when pumped from the ground). The crude must undergo a variety of refining processes before yielding base stock suitable for use in engine oil. Undesirable components such as wax, sulfur and nitrogen compounds must be removed. Unsaturated hydrocarbons must be extracted or converted into more stable molecules. Crude is first separated by vacuum distillation into a series of fractions or viscosity ranges. The fractions intended for base oil production are processed further using various combinations of refining processes, such as:
- Solvent Extraction- separates the naturally occurring saturated and unsaturated hydrocarbons.
- Hydrofinishing- removes some of the nitrogen and sulfur compounds, improves color, oxidation and thermal stability of base stock.
- Hydrotreating- converts some of the unsaturated hydrocarbons to saturated hydrocarbons to help improve yield prior to solvent extraction. This process also helps remove of large portion of sulfur and some nitrogen compounds.
- Hydrocracking- a sophisticated process in which molecules in the base stock fraction are rearranged into the desirable saturated hydrocarbon molecules. The yield of saturated molecules is much greater than that achieved with hydrotreating and solvent extraction.
- Hydroisomerization- when used along with hydrocracking, can transform the molecules of the base stock fraction into the most stable form possible.
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- are used to maintain engine cleanliness, keeping the various contaminants in a fine suspension and preventing them from settling out on vital engine components.
- Rust and corrosion inhibitors- are added to protect the engine from water and acids formed as combustion by-products.
- Antioxidants- are added to inhibit the oxidation process, which can result in oil thickening and sludge formation.
- Anti-wear additives- form a film on metal surfaces to help prevent metal-to-metal contact.
- Viscosity modifiers and pour point depressants- help improve the flow characteristics of motor oil.
Now that you know what motor oil is, how it is made and what it does, here comes the most confusing part of all: grades. In order for motor oil to perform its major function - lubrication - its viscosity (the measure of it's thickness or resistance to flow) must be capable of holding up under your engine's extreme temperature conditions. Oil thins when heated and thickens when cooled. Choosing the proper viscosity grade for the ambient temperature of your geographic location becomes vitally important.
A monograde is an oil whose viscosity is defined at only one temperature, either high or low. A multigrade must meet both high and low temperature viscosity requirements simultaneously. This makes multigrades an easy and popular year-round choice for drivers who experience hot summers and harsh winters. They are easily recognized by the dual viscosity designation (i.e. 10W-30 where the 10W is the low temperature, or winter designation and the 30 is the high temperature designation). It is the viscosity modifier additive that produces a thickening effect at high temperatures but is dormant at low temperatures.
Information concerning the performance, viscosity grade and energy conserving properties of an oil can be found within the API Service Symbol, also known as the "Donut". This symbol displays the API (American Petroleum Institute) Service rating, a two-letter classification that identifies the quality level of the motor oil and the type of vehicle it is suited for. The first letter "S" indicates the oil is appropriate for "spark ignition" or gasoline engines. The first letter "C" indicates the oil is intended for "compression ignition" or diesel engines. The second letter in each category indicates the performance level of category. For the "S" categories, the performance level increases as the categories go through the alphabet. However, the same is not true for the "C" categories as the types and intended application range for diesel vehicles vary greatly. It is important to refer to the owners' manual for appropriate performance recommendation.
In the center of the donut will be the SAE (Society of Automotive Engineers) viscosity classification. The bottom of the donut is reserved to convey the energy conserving properties of the oil as determined in a standard industry test.
If an oil meets both the latest "S" API service category and the current energy conserving standard, it is also able to display the API Certification Symbol, known as the "Starburst". The Starburst will always be found on the front label.
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