I have a jar of the oil that was in my car for 7500 miles of mostly highway driving, and a jar of fresh oil. Both were sitting in the freezer at about -20C overnight. I can't really say there's any big difference in the way they move around in the jar. I now have them wrapped in Al foil to make sure they are at exactly the same temperature. The fresh oil seemed to make the engine run smoother, so I suspect it has thickened, but I don't think the cold weather performance has suffered much, if at all. I could spend $50 to have it CCS tested at a lab.