It surely shouldn’t be. The base stock weight in both those oils is 5. The only difference are the additives. They stay coiled up and have zero effect on thickness until the oil gets hot.
Yes, they’re coiled, and uncoil with increasing temperature. But what I can find indicates this happens gradually, not an ‘on/off’ effect. That’s why you can notice the difference, even at room temperature. Also, the ‘base oil’ is different between Mobil1 and Rotella, so their basic behavior with temperature will be different, aside from how the viscosity index improvers behave.
True…never said anything different.
There should not be noticeable difference at room temps. Both have a viscosity rating index of 5.
Who says? They should flow the same.