sorry the below information i can't write it in Arabic.
the below information are very heavy please read slowly.
Engine oils are classified as follows:
1- According to viscosity grade of the SAE (Society of automotive engineers).
2- According to performance of the API (American petroleum institute).
First we will talk about the viscosity grades:
NOTE: the oil viscosity depends on the temperature, so when we measure the viscosity of an oil we must state the temperature at which we measure that viscosity.
Engine oils are of two types:
1- Mono grade engine oil = means engine oil has a specific viscosity at a specific temperature.
2- Multi grade engine oils = means that the oil will meet different viscosities at different temperatures
what is written on the gallon?
you will find that the engine oil viscosity grade is written according to the SAE standards as follows:
SAE 40 or SAE 50.
the above example says that this oil is mono grade and its viscosity grade is 40 or 50.
so what are the viscosity grades ?
SAE make a list of viscosity grades, the grades are splitted into two groups:
one are for the high temperature countries and all are measured at 100 degree Celsius.
these grades are: 25, 30, 40, 50, 60
and the other grades are for the cold temperature countries and are measured at low temperatures as 0W, 5W, 10W, 15W, 20W. W means winter.
note these grades are not the measure of the viscosity, it is a Category but as the grade is high the viscosity is high.
now back again to the SAE 50
this oil is a mono grade , where it will give us a specific viscosity at high temperature and is used for cars working in high temperature countries.
so now if we are in Moscow, we will buy an engine oil with an SAE grade of 5W or 0W for example.
and if u drive your car from Moscow to Ryadih or Kiwuat, what will you do? you will change the oil to SAE 50 or even 60 for example.
from the above example it is clear now; what is the multi grade engine oil , it is for example SAE 5W-40; so we have an oil that will work in Moscow and in Kiwuat in the same time and no need to change that type of oil between countries or between seasons of cold winter and hot summer.
Secondly the API standard:
the API make a standard for engine oils
you will find API SL/CH-4
the first letter means:
S is for Sprak ignition engines; means for gasoline engines.
C is for Compression ignition engines; means for the diesel engines
the second letter means the grade;it starts from A to M for the gasoline engines and starts from A to J for the Diesel engines
so you buy a gallon of engine oil and it has an SAE 50 and API SE/CF-4
this means that this oil will work with Gasoline and Diesel Engines and it has a viscosity grade of SAE 50.
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