Redstone Engine Edit
The simplest of engines in Buildcraft. Can only be used in conjunction with an extraction pipe (wood or emerald) to pull items from the inventory the pipe is connected to. It can not be connected to a kinesis pipe. It does not consume fuel; it only needs a redstone signal to function. Unlike the other engines, this one doesn't burn out and can run indefinitely if it's connected to an extraction pipe.
When you attach a redstone engine to an extraction pipe it will extract 1 item every 0.8 seconds when it's running at full speed, which is when it glows red. For reference, a vanilla hopper extracts 1 item every 0.4 seconds. You can, however, attach up to 4 redstone engines to an extraction pipe to extract items or fluid more rapidly. One engine will extract 1 bucket of fluid every 5 seconds.
The redstone engine can be replaced with a gate equipped with an autarchic pulsar expansion
Stirling Engine Edit
The next step up is the Stirling engine. This engine can power machinery such as the Quarry, and can be connected to kinesis pipes to work in unison with other engines. This engine has an UI showing the power output, power storage, and heat.
It produces 10 RF/t when it's running optimally at 100,02°C. If there's nothing to power and the engine is left on, the temperature will gradually build until the engine fully overheats at 250°C. When that happens it needs to be picked up and replaced to resume operation. It does not explode.
If the engine overheats past 105°C and then power flow is resumed its power output will be reduced to 3 RF/t. It will operate at the temperature when the power flow was resumed. If it overheats past 133,32°C, and then power flow is resumed, the engine will cool and proceed to function at 133,32°C. The power output will be reduced to 3 RF/t. To restore full power output the engine needs to be turned off so it can cool to below 100,5°C, after which it can be turned on again.
Gates can be used to keep the engine from burning up completely, but they won't save them from overheating as the engine only turns yellow at 135°C. You can however include a manual override in case it does happen. See <tutorial>.
This engine will move 16 items every 0.9 seconds if you decide to use it as an extraction pipe.
Combustion Engine Edit
The combustion engine is the most powerful here. It can produce 30 RF/t on oil and 60 RF/t on fuel. It needs a constant supply of water to remain cool, otherwise the temperature slowly starts to rise until it reaches 250°C at which point it overheats and stops working in the same manner the Stirling engine does. Its power output remains the same until it overheats completely. It does not explode. When the engine is turned off, even when it hasn't overheated, it needs to cool down all the way down until it can be turned back on again.
The engine is at its maximum potential the moment it turns on, and does not consume water until it reaches 100,01°C. It uses about 1 mB of fuel per second, and a bucket of water every 10 seconds at peak power.
This engine will move 2 stacks of items every second if you decide to use it as an extraction pipe