What do you mean by 20w40 engine oil?

Answer 1

Dear All,

I would like to add some information regarding the engine oil grades

Firstly, the engine oils when they mean SAE 20W40 the numbers 20 and 40 aren't actually referring to any temperatures here they are actually Saybolt universal seconds its actually a unit of kinematic viscosity the details of which can be found in this link

Saybolt Universal Second - Wikipedia, the free encyclopedia

Now a question might arise in your mind that the link isn't specifying any details about it being used as the designation for the SAE grading system. Actually now, Saybolt seconds are considered obsolete, but they have been used traditionally in the petroleum industry and are common in technical articles. Most of the web pages describe them as viscosity grades only.

As far as the gradings go in a multi grade oil, the grades 20, 30, 40, 50 are obtained from the viscosity readings at 212degree F (100 degree C) and for winter grades at 0 degree F(-18 degree C) used to see the pour point of the lubricant.

The Saybolt furol viscometer is the one that is used to test the oil you put in your car. Fural is an acronym forFuel and road oil.

For a good lubrication the lubricant must actually make up a separating layer and not thin out. Infact it should be viscous enough to form this layer. Lower the viscosity greater the wear. The well known fact is that viscosity changes with temperature. Synthetic multi grade oil 20W40 basically will thin out more at high temperatures than the 20W50 oil(definitely not at 40 degree C).

the values preceding the "W"(meaning winter) are to be low especially at cold startup when the lubricant should be able to flow (thin) for this pour point depressant additives are used in the oils. So for approximate engine oil grade use the chart given by your vehicle manufacturer in your manual book.

Answer 2

No