One main advantage of the better 0W-XX oils is that they have higher VIs than 5W-XX oils. A good example of this is M1 0W-40 with it's 185 VI and an even better example are the Japanese 0W-20 oils with their 200+ VIs. In the later example they are a good 30% lighter even at room temperature and more than 50% as you approach the freezing mark compared to a typical 5W-20. So you don't have to wait for temp's below freezing to see real benefits. That temperature/viscosity graph is pure [censored]. All oils go parabolic eventually at cold temp's. To see what a proper gragh looks like click on the following: http://www.widman.biz/English/Calculators/Graph.html 0W-XX oils have to use better base oils than most 5W-XX and heavier oils, consiquently their NOACK percentages are no higher and often lower for the same oil weight. There are no technical disadvantages to 0W-XX oils today over 5W-XX oils, they are superior lubricants. The only problem is that they are not as universally available and can cost more.
Originally Posted By: river_rat
It has to be pretty cold to make that much difference, in my opinion. I borrowed this from a post by spin9k over at the RX8 Forums:
Originally Posted By: spasm3
i've always wondered what temperature it took to see the diff in a 0w and say a 5w