Heavier weight oil as the engine ages is an age-old myth. The theory is that heavier weight oil produces a thicker oil film to help piston rings seal better as they age. That’ part has a tinge of truth to it— it does provide a thicker film. But that ignores the downsides to heavier weight oil. Optimal oil weight is based on bearing clearances and using a higher weight oil has negative affects on oil flow through bearings. Using a heavier weight oil actually reduces heat transfer from the bearing clearances. In addition, the internal friction of heavier oil actually creates more heat, which is the last thing you want. So using a heavier weight oil increases engine wear. How much? That depends on how much heavier you go. A switch from 20 to 30 weight is probably negligible. But 20 to 40 would not be good. Use the oil the carmaker recommends, not some self proclaimed oil expert friend who really doesn’t know jack about tribology.