"Grant Erwin" wrote in message
...
I don't think it will work. KOH is about like NaOH, in other words a
strong base.

Hot caustic baths are what commercial engine rebuilders use to "hot-tank"
engine blocks. Local services often offer the same thing, for small-time
rebuilders. There are commercial hot-tanking solutions but they are
basically lye, if you'll forgive the pun. g

They often advertise it as a way to remove rust. But it doesn't strip rust.
What it does do is clean out the oil and some other crud trapped in cooling
passages, as well as varnish and oil in the oil galleries. Some of the flaky
rust in an old engine is trapped there in mungy old oil that got into the
cooling system, so some rust does, incidentally, come out when you hot-tank
an engine.

To remove attached rust you either need to remove it mechanically or with
acid, as you say. I'd be wary of using acid in a cast-iron engine because it
will be hard to remove. Iron has a lot of pores where graphite flakes out.
Maybe someone has experience with it and knows how it works out in practice.
I'd just be darned sure to flush it out with a mild alkaline solution if I
were going to try it.

Ed Huntress