The Stovebolt Site Forums The Shop Area Engine Shop oil level

I don't profess to be expert on the subject of multi-viscosity oils but I can tell you that the 10-30 I drain hot is a LOT thinner than the 10-30 I pour in cold. My understanding of m-v oils is that the higher number means they provide the "protection" of the higher number straight weight oil not that they obtain the thicker viscosity. Do I understand wrong? After decades of changing oil and watching what I put in and drain out I doubt it.