Note: Lava is no longer usable as a source of fuel.
One Combustion Engine can adequately power all BuildCraft machines, however two are required to fully power a Quarry or a Refinery. The Combustion Engine is fueled with Lava, Oil, or Fuel, but unlike the other engines, it must be cooled with Water or the engine will overheat. It can be filled with Water using Fluid Pipes or Buckets. It needs a Redstone signal to operate. Water Pump Pipes can be used to constantly pump water into the Combustion Engine to prevent overheating. Coolant will also work, but will require constant refilling if using Fuel as fuel.
The amount of RF/t that the Combustion Engine produces depends on the type of liquid that is used: