heat in the engine rises
Not unless you are melting it, it doesn't!
when conducting heat through the engine, including the application of heat at the sump, heat rises
Complete tosh. The molecules of metal in the engine are not free to move about like air or water (or other fluids, e.g. molten metal) and change density.
Therefore there is no lowering of density, and no heat rising in the metal of the engine.
If you are able to show me bubbles of pistons rising through denser, cooler cylinder heads then I will believe that metals can heat via convection!
FBW