There are two rreasons that we use 0W20 oil. #1 Emissions, The EPA states that each manufacture has to have an overall fleet emissions number and one of the ways they get this is by utilizing thinner oils. we don't really need to go into how this works. #2 these engines are very close tolerance, they need a thinner oil to get through the oil passages and all the areas that need to be lubricated. (This also plays into the emissions and efficiency of the engine). If you start messing with the viscosity of the oil, you risk damaging the internal components. If you notice, GM does not give you any range of viscosities to use based on external temperatures as they do in other engines. My opinion, which is mine alone, is that anything that promotes doing anything to the engine oil that will change any properties of what is designed by the manufacture is nothing but snake oil and a marketing scheme to make money.