help with cooling system

[2.9._ranger]

i took my engine apart to replace all gaskets and clean it, while cleaning the block i checked the coolant passages and there are deposits of some type of brown gunk that has built up around the cylinders in some places there is a pile of it that fills half the passage, it didn't have any overheating problems before taking it apart but i want to clean this stuff out, does anybody know of a wa i can clean this stuff out without having my block boiled?

 

[JerrySab]

Had the same issue! with blocked passages and mountains of rusty crusty crap. Take this with several large grains of salt. Maybe good plan of attack, maybe not? I'm happy with the outcome, but still mid-project.

I poured evaporust into the block, being as careful as possible to not slop it into the oil passages, but I'm sure I wasn't perfect. let it sit, then pulverized the crap with long brass engine brushes on the end of drill, then sucked it out with a narrow nozzle on the wet vac. wash rinse repeat. There may be smarter, prescribed ways to do it, but this made sense to me and the passages are much clearer now.