Can 5W-30 flow at temperature X exactly like 0W-20 at temperature Y?

[Javed]

X = 30° f
Y = 10° f

Can the difference be that big, like 15 degrees?

In this graph it looks like roughly 5 degrees. The warmer it gets the less the difference.

 

[Jetronic]

I believe the graph uses degrees celsius. so 5 °C works out to 9°F

 

[SubieRubyRoo]

Yes.

 

[ka9mnx]

That is called Viscosity Index and is widely variable depending on the base oils used and Viscosity Index Improver additive.