Heck, I've wiped overspray off with a rag soaked with gas. If it's more than that will remove, it's really more than overspray. Of course if you do that, you need a bucket of Dawn and water close by to wipe the gas off the freshly exposed paint. I've told people about that trick before and they look at me like I'm crazy. But I can tell you from experience, more body shops use that trick than you know.
Now, it will remove everything if the overspray isn't real bad.....including any wax coating that may have been on the original paint.....I doubt seriously though there was wax on the paint in the engine compartment.
What I would do if test it on an inconspicuous spot that has some heavy overspray on it and see what kind of results you get. If the gas won't wipe it off, the sandpaper might be your next option.
