a little disagreement with synthetic oils needing no VII (viscosity improvers)
This is an over simplification, but what you are comparing are the viscosity of the oil measured at freezing and at the boiling point of water.
The 20w (winter grade) represents viscosity of the oil measured at freezing.
The 50 represents the viscosity of the oil measured at boiling 100c 212f or whatever.
There are some synthetic oils that may have a rating of 20w20 containing no VII.
However I really doubt any synthetic oil can achieve a 20w 50 rating with no VII.
However synthetic oils contain no parafin wax so much less VII is needed than in mineral oils.
However in my career I blended fuel oils and diesel oil for viscosity, pour point etc. I never worked with motor oils so I may be on a slippery slope.
This is an over simplification, but what you are comparing are the viscosity of the oil measured at freezing and at the boiling point of water.
The 20w (winter grade) represents viscosity of the oil measured at freezing.
The 50 represents the viscosity of the oil measured at boiling 100c 212f or whatever.
There are some synthetic oils that may have a rating of 20w20 containing no VII.
However I really doubt any synthetic oil can achieve a 20w 50 rating with no VII.
However synthetic oils contain no parafin wax so much less VII is needed than in mineral oils.
However in my career I blended fuel oils and diesel oil for viscosity, pour point etc. I never worked with motor oils so I may be on a slippery slope.