I found this on the internet about engine block casting techniques. No one here has stated whether the rods that they've seen in their blocks are steel or aluminum.
The core shown below provides the space for water jackets around the cylinders. The core has being painted to seal the gas formed during the casting process within the core. And the pink colored ends are not painted to let the gas escape to the out side. Aluminum reinforcing rods are used to give more strength to the core. These rods get melted due to the molten metal poured during casting.
View attachment 1715836489
