0W20 vs 5W20 base oils

[kschachn]

Then the question is why some cars call for 5W20, not 0W20? Or vise versa?

Whatever the reason it is not because of startup wear since that's relatively unimportant. All oils provide sufficient MOFT at startup since all are very thick. Many 0W oils are thicker at most temperatures than their 5W counterpart, only at temperatures below -35F or so are they guaranteed to be thinner. But at these temperatures both are very thick.

Some people have speculated that one reason for listing a 0W rated oil in the owner's manual is that these oils are nearly all synthetic and therefore can meet the manufacturer's OCI targets. Who knows if that is correct.

 

[ka9mnx]

Cost and availability. At one time 0w-20 was hard to obtain and pricey.

 

[nostradamus]

BOV (base oil viscosity) is indeed thicker with a 5w-20 than a 0w-20. 5w-20 oils have less VII and lower noack as well. Look at Gokhan’s work with A_Harman index. 5w-20 oils are superior to 0w-20

 

[OVERKILL]

BOV (base oil viscosity) is indeed thicker with a 5w-20 than a 0w-20. 5w-20 oils have less VII and lower noack as well. Look at Gokhan’s work with A_Harman index. 5w-20 oils are superior to 0w-20

That's a sweeping generalization and there are numerous exceptions to that. A few examples:

M1 HM 0w-20: https://pqia.org/mobil-1-sae-0w-20-...0&utm_campaign=April+7,+2020&utm_medium=email

Noack 9.7%

Ravenol DFE 0w-20: https://www.ravenol.de/en/product-range/motor-oils-for-passenger-cars-1/ravenol-dfe-sae-0w-20/

Noack: 7.6%

Castrol Edge 5w-20: http://pqiadata.org/Castrol_Edge_5W20.html

Noack: 12%

Supertech 5w-20: http://pqiadata.org/SuperTech_5W20.html

Noack: 11.7%

 

[blufeb95]

BOV (base oil viscosity) is indeed thicker with a 5w-20 than a 0w-20. 5w-20 oils have less VII and lower noack as well. Look at Gokhan’s work with A_Harman index. 5w-20 oils are superior to 0w-20

That fails to account for things like even in the same product line a manufacturer may use hydrocracked crude as the majority base oil in their 5w-20 while they may use majority PAO in their 0w-20 product as is the case with Mobil1 Extended Performance. So it's hard to say which has less VII and I don't have the noack data.