Originally Posted By: dpaldino
Still don't get why an 0W-20 doesn't pour as well as the 5W-20 oil. I could see if they were different brands or if one was synthetic and the other dino. If you take the exact same oil brand but different grades, I would expect the thinner oil to flow, pump, pour and lubricate more easily than a thicker oil at low temperatures but that doesn't seem to be the case here. If I put 0W-20 in my engine, I would expect it to perform better at low temps than a 5W-20. If that is not the case, then what advantage would a 0W-20 oil be providing over the 5W-20 grade?
I don't blame you for being confused. After all this site, as well as many others, always talks about flow and protection and most equate better flow with better protection. This is true in a splash lubricated system, totally false in 100% of automotive applications that are even remotely modern.
0W means the oil will be pumpable at -40C
5W means the oil will be pumpable at -35C
10W means the oil will be pumpable at -30C
15W means the oil will be pumpable at -25C
This means that the oil will be able to flow into the oil pump inlet and then be pumped throughout the system. Better flow means nothing because the oil only has to flow into the inlet at the same rate the pump displaces it. Basically it has to keep up with the pump. It is the pump that dictates the rate of flow, so it makes little difference if one oil flows better than the other, because a positive displacement pump will move the same rate of fluid regardless of its viscosity.
Centrifugal pumps change the rate of flow with fluid viscosity, not positive displacement pumps.
And before anybody says "what about the oil return? It's gravity", well, so is the feed to the oil pump inlet