I was told when I was in automotive school that when they cast the block they use sand casts. Due to the fact that the block is cast around sand, alot of it is left inside the engine block, and so holes are cast into the block, in the low points of the water and oil jackets so that when they get the engines out of the cast they can high pressure wash them out and get all the sand out, and they stick the plugs into it to keep your water from running out, lol also they are supossed to pop before freezing, but I gooed the hell out of them because we are forcing high pressure water into our engine blocks when we use them for jet boat use, most likely more pressure than it would see even under the pressure that a sealed cooling system would generate so I didnt want them coming out. Plus if one comes out at the river im screwed lol.
