Sure does work I've used it on my car and my friends RX7, he had a bad vacuum leak on the underside of his intercooler and it found it.

As far as it being safe, it's safe to breath so I can't imagine how it would hurt an engine.

 

it's just a machine that you creates smoke. You pull a vaccum hose and hook thee machine into it turn it on and look. Some have a light that helps you see the smoke. You can use them for oil leak, vaccum leaks, exhaust leaks, and evap leaks.
http://buy1.snapon.com/catalog/item....re&dir=catalog

 

I've seen them used to find gaps in weatherstripping around doors as well.

 

alright, i have a friend that has one, i might just give it a shot. . if not i'll just build one