Posted by David Sherman on Wednesday, August 11, 2004 at 3:27PM :
In Reply to: Re: How do you clean water passages? posted by Chris In Idaho on Wednesday, August 11, 2004 at 12:11PM :
Actually, that's not such a concern with hardware store (29 deg) muriatic acid as with anhydrous sulphuric acid or something else equally strong. I have done it both ways in small amounts and nothing bad happened. I tend to use hydrochloric for rust-removal just because it's the only strong acid that's cheap and easy to get. Battery electrolyte isn't strong enough, and most everything else requires buying from a chemical supply house at high cost and often they won't even sell it to you unless you're a known big company with an account, due to all the regulations targeted and mad bombers and amateur drug makers.
The other neat way to clean up rusty steel, and reduce some of the rust back to a tight black oxide "blueing" is the electrolytic method. It requires only a battery charger, a piece of scrap iron, a plastic container, and a little washing soda. Unfortunately it won't do inside passages, which is exactly what needs cleaning in an engine block. It's absolutely the best for old tools, though. I first tried it on a bunch of very rusty but good old Armstrong lathe tools and when they were done and rinsed off and oiled, they looked like nicely-blued gun metal. All the loose rust fell off, and the tight rust converted back to black oxide. Where there were spots of original bluing on the tools, the treatment didn't even remove it, unlike an acid pickle that would strip it all down to bright etched steel that would begin rusting as soon as it came out of the tank.