I've painted a bunch, like Dave has, with epoxy primer and catalyzed enamel for the top coat. It is far superior to any spray can engine enamel and lasts for years and years. Engines only get up to the 180+ temp range, which isn't all that hot, so it doesn't burn off at all. It is the only way I will ever paint any engines I do in the future too. The key is the epoxy primer.

Don