Originally Posted By: Clevy
Alright.
So because a higher vi oil is closer to optimal viscosity and is thereby easier to pump and moves faster cold.
A lower viscosity oil is harder to pump,has more resistance to flow until hot which adds to total friction and with therefore heat up faster because it requires more energy to get to optimal,and that energy is absorbed by the oil as heat.
Am I close?
So the example above then which would be more desirable of the 2 options given?
The lower viscosity index oil or the higher,but thicker one.
Assuming that you aren't at the limits of pumpability, and it's a plain, normal start at reasonable ambients, the oil pump will shift exactly the same amount per revolution for either low VI or high VI oil.
if both are in bypass on cold oil, the heat applied by the oil pump is exactly the same.
It's the work done in shearing the oil in the bearings and against cylinder walls that means that the oil that's thicker has greater drag.