Cleaning scale from coolant passages

[danielsprague]

Hi

I've got my block stripped down. I'm going to make a DIUY hot tank to get rid of the slugde and muck, but how can I clean out the water channels? They seem to be quite mucky at the bottom of the block, though clean towards the top.

Any ideas? vinegar doesn't shift it, and i can't get my hands on any strong caustic soda...

Cheers

Daniel