Since I am considering switching to straight grade oil (just to see what the used oil analysis results are--at least at first), I did a Freezer Test™ last night with Valvoline 30 and Rotella T 15w40. My freezer stays between 0F and 10F. I used two small clear plastic Dixie cups. This morning both oils were equally fluid. I could detect no difference. Both would pour relatively easily. The 5w30 Shell I used as a reference was thinner and would pour more easily, but the difference wasn't as great as one would assume.
My observations are backed up by the vis calculator:
Viscosity of Valvoline 30 @ 10F = 4079.7 cSt
Viscosity of Rotella 15w40 @ 10F = 4635.6 cSt
My observations are backed up by the vis calculator:
Viscosity of Valvoline 30 @ 10F = 4079.7 cSt
Viscosity of Rotella 15w40 @ 10F = 4635.6 cSt