Hi everyone. Been lurking for years. I already feel like I know most of you and know quite a bit about oil and the site. Feels good to finally make it official. I have a question about shear stability. Please correct me anywhere if I'm wrong. To my understanding, the smaller the viscosity (number) spread between the winter rating and 'hot' (100Â°C) rating, the more shear stable the oil is. So in theory a 5W-20 should be far more stable than a 5W-50. Right? That said, let's go off topic a bit and talk about the winter viscosity rating of oil. The 5 in 5W-20 is the winter rating. I'm fairly sure that the "5" at a very cold temperature is actually far more viscous than the "20" at 100Â°C, contrary to what most people think. Oil 'thins' as it gets hotter. I'm assuming I'm correct so far? So now my real question: If the first two statements are true individually, how is it possible that both are true at the same time? I would think based on the above statements that a [theoretical] 0W-60 would be the most shear stable oil out there, and a 0W-16 would shear like crazy. 0W-60 would be 'thin' (which is still kinda thick) at freezing temperatures, but only thin a small amount to a 'thick' 60 at 100Â°C. A 0W-16 is still 0W in the cold (which once again I presume is kinda thick compared to the viscosity at 100Â°C). The change in viscosity over the temperature spread seems to be less with a 0W-60. It doesn't have to thin much at all. Whereas a 0W-16 has to go from a thicker viscosity when cold to a crazy thin 16 viscosity at 100Â°C. Perhaps you all can clear this up for me? Thanks!