4. SAE CLASSIFICATION

In the SAE classification, oils are identified according to their viscosity, not taking account of any other qualitative feature.
The first number refers to cold viscosity for winter use (symbol W = winter), while the second one considers hot viscosity.
The choice criterion must take account of the minimum environment temperature the engine will be subjected to for winter and of the maximum operating temperature for summer.
In the case of sporty and urban driving or when the air temperature is high, the engine undergoes high temperatures that accentuate the phenomenon. It is therefore fundamental to use an oil that stays sufficiently fluid, to distribute well in the engine, protect the mechanical parts and facilitate ignition.

Monograde oils are generally used when the operating temperature does not vary much.
A multigrade oil is less sensitive to temperature.
Multigrade oils are a particular class of oils, which have a viscosity curve that complies with several SAE numbers. For example a 15W-40 oil covers the 15W-20/30/40 grade range.
 


SAE TABLE OF ENGINE OIL VISCOSITIES (SAE J300 - Society of Automotive Engineers)
 


SAE GRADES FOR ENGINE OILS RECOMMENDED IN RELATION WITH THE OUTSIDE TEMPERATURES


 ENGINE OILS FOR CARS


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