SAE viscosity classification
When the temperature of oil is high, its viscosity decreases (becoming free of stickiness, like water) and when the temperature is low it has greater viscosity (becoming sticky like honey).
When the temperature of oil is high, its viscosity decreases (becoming free of stickiness, like water) and when the temperature is low it has greater viscosity (becoming sticky like honey).
With low viscosity there may be breaks in the oil film, making it easier for parts of the engine to seize.
Conversely, if this viscosity is high the resistance increases, making it more difficult to start the engine and increasing the amount of power loss.
Conversely, if this viscosity is high the resistance increases, making it more difficult to start the engine and increasing the amount of power loss.
The SAE viscosity classifications display oil viscosity using numbers, with a smaller viscosity number meaning an oil has less viscosity.
Those indicated as SAE20, SAE40, etc. are called single grade, and are usable in a narrow temperature range.
Those with a spread, such as SAE 10W-30 or SAE 20W-40, are called multigrade and can be used in a wide temperature range.
Currently, multi-grade engine oils are more commonly used for automobiles.
Those indicated as SAE20, SAE40, etc. are called single grade, and are usable in a narrow temperature range.
Those with a spread, such as SAE 10W-30 or SAE 20W-40, are called multigrade and can be used in a wide temperature range.
Currently, multi-grade engine oils are more commonly used for automobiles.
As an example, the "W" in 10W-30 stands for winter. Smaller number means, it is more difficult for the oil to harden at low temperature.
The "30" represents viscosity at 100 deg celcius. Higher number means the oil won't become too soft at high temperatures.
The "30" represents viscosity at 100 deg celcius. Higher number means the oil won't become too soft at high temperatures.
API quality classification (API service classification)
Since the oil is violently agitated at high temperatures, an environment is created where the oil can be oxidized easily by the oxygen in the air.
When the oil is oxidized, sludge (deposits of altered components), etc., are generated, decreasing lubrication performance.
Since the oil is violently agitated at high temperatures, an environment is created where the oil can be oxidized easily by the oxygen in the air.
When the oil is oxidized, sludge (deposits of altered components), etc., are generated, decreasing lubrication performance.
In addition, most of the engine parts are made of metal and rust is prone to occur, so the oil is required to have high rust prevention performance as well as its quality should not change.
The API quality classifications are the most commonly used standard for oil quality. Since viscosity and quality required vary depending on the engine characteristics and use environment, it is essential to use oil with the specified standards.
The API quality classifications are separated based on quality and usage, determined by API test methods.