What is this stuff in my block?

toolmanmike said
I flushed my 273 years ago shortly after buying it after replacing a rusted out core plug. I unscrewed the small drain plugs and prodded with a pocket screwdriver to get the gunk to flow and finally got a steady stream. After repeated flushing I thought I had it pretty clean until I took the engine apart for rebuilding. The coolant passages were filled to the bottom of the core plug holes with core sand and sludge. It took me an hour or so with a hose and a coat hanger to get it all out. tmm

Yes, you don't know if your block will be a good one or one with a bunch of "crap" in it like TMM's.

The best way to make sure is to clean it like Mike. Pull the plugs and make sure that the water jacket is not plugged. If it's plugged, then scrape it out with long screwdrivers/coat hangers.

You have to check each block. I've had good clean ones, and some gunked up like Mike mentioned.