Flush or transplant?

I de-rust a lot of parts with it. I'm not sure I'd feel comfortable running it in an engine though. The stuff makes nasty fumes. Even the fumes will start rusting metal parts. I ruined an aluminum part by leaving it in the acid too long.

I have heard of people using EvapoRust inside the engine. You run the engine until it's up to temp...shut it off and let it sit over night.