Engines, in general, work underwater. So long as they have air and fuel coming in, have somewhere to put the exhaust, and some sparks to light the fires, they'll keep running.Originally Posted by VXD959
Exhaust is under pressure, so that one's okay. The air intake is on top of the engine, so that's usually okay up to a point. Electrical is the last issue, and one of those fun scientific truths is that water is actually not a very good conductor.
Still, most engines that are entended to go underwater are diesel -- no spark plugs means no water/electrical problems.