Regarding the potential for an engine to come out grey. The engines I cleaned were a mix of Webra, O.S., and Enya, 2 stroke and 4. They all look about the same to me when done. Whatever the color, which I haven't seen as anything unusual, when the results were weighed against what I had going into it, there is no question regarding the benenfits of the process. I did squirt them down pretty good with WD-40 and blew them out with compressed air as part of my process. Maybe that has something to do with the resulting color? Dunno. Based on my experience with 10 or 12 of these to date, I sure wouldn't let the resulting color slow me down any.

Regarding the cooking temp, I'm working in a well ventilated area. The same one I'd be working in with any other chemical (like gasoline for instance). I did boil some stubborn parts for a couple of hours - and it does emit some pretty rancid fumes I wouldn't be sniffing - but the AF process is much more effective that way if you require it to be? Not sure I'd walk away from that process overnight though.... FWIW