They are air cooled you don't get steam

No, but you can getting something worse. Back in H.S., a friend and I were driving up a long grade into the mountains when the bug (thrashed baja variety) starting losing power. We pulled over to investigate. Problem was, it was twilight and getting dark fast. So my friend, genius that he was, took out a Bic lighter and starting looking around. It turned out that the mechanical fuel pump diaphragm had broken, which tends to dump some gas into the case.

I'm standing there watching, he's bent over with the lighter up close when... WHUMP! Some fumes ignited. I swear I could see the case seem to expand at every seam. He landed several feet back on his ass, and I laughed till I had tears in my eyes.

Live and learn.