The normal procedure for preparing an engine block for other work is to get it clean first. In "ye olden days" I would have simply taken it to someone with a boil out tank and be done with it. Since the state of California has outlawed this, I now have a nice clean block with rust still present in the water jackets and need ideas on how to remove it.
My thought is to place the block on my bench with the water outlet blocked and fill the jackets with something like CLR, then drain. Is there something better or more effective I can use that's still safe? Muriatic acid is out as far as I'm concerned....effective stuff, but I had a bad experience with it once and ruined an otherwise useable part. Sandblasting is out also, since I can't reach a lot of the interior and don't want any sand hiding inside afterwards......
This fine gentleman used CLR with good results:
This page on cooling includes a little bit about flushing and cleaning. http://dauntlessgeezer.com/DG96.html
Be careful using a corrosive on cast iron and watch it very carefully to monitor its' progress and affect on the jacket walls. Unlike steel, the many imperfections in cast iron causes the corrosive to, not only attack the rust, but the cast iron as well, which makes cast iron corrode much faster than steel and since the walls of the block are thin to begin with, there is a very real danger of rust through, but this danger will be minimized as long as you don't leaved it and watch it closely. Be sure and neutralize the corrosive with a solution of baking soda and heat the block with a heat gun for several minutes until it is several hundred degrees to prevent steel embrittlement which is caused by the introduction of acid into the metal. Jim Patrick
How far is it to some shop in a neighboring state that still allows boil out tanks?
But your babbitt will be lost in a boil out tank, maybe it's going to be rebabbitted anyway?
A piece of speedo cable in an electric drill can also clean loose rust in the water jackets.
Have you tried electrolysis derusting.