The Steam Engine is stronger than DC Electric Engines and Wind Turbines. It will run constantly when given a heat source (lava or fire) below it and water on any side of the engine. Adding a lava source is not a good idea, for it will cause the engine to explode at temperatures over 180C. Remember to add a coolant such as water or ice if you do choose to use lava. When the temperature is high enough, a steam engine will produce 32Nm at 512 rad/s (16.384kW).
The steam engine will not work for long if not provided with a source of water, either by piping it in to the rear of the engine, or manually adding buckets via the engine GUI. Manually adding buckets is not reccomended due to the rate that the engine uses water. Detonation of the engine will occur when the engine reaches 180C and will damage your surrounding structures.