The Magmatic Engine consumes lava to produce BuildCraft energy (Minecraft Joules). Will reduce power output (and fuel consumption) if not enough energy is being consumed. It will shutdown if it can't output energy.
Converted via Energy Bridge this Engine produces over 40.000 EU per Bucket (more than double of the Geothermal Generator from Industrial Craft).
Using a crescent hammer or a BuildCraft wrench you can turn it back on when it overheats. Unlike other engines such as the combustion engine or the stirling engine, magmatic engines do not explode they just stop working.