Redstone engines are the cheapest of the type of Engine and as such are the least powerful of the three types of engine.
Redstone engines, like all other engines, gain speed as they heat up, which increases their energy output per second. Unlike Combustion engines, they will never explode on running hot, except when not powering anything (see below). In fact, they produce more power when becoming orange-blinking-red and it is not advised to turn them off unless needed (again, see below).
Like the other engines, the redstone engine can be turned on and off using a redstone signal, and requires an active signal in order to activate.
Redstone engines are most often used for powering things like wooden pipes when it's not necessary to move many items at once because they are cheap to produce and maintain. The minimum configuration takes only two blocks: the engine itself and a lever or redstone torch.
In addition to wooden pipes, redstone engines are able to power two basic machines directly, the pump, and the mining well, though they require 2 or more running hot to have any effect.
All engines in Buildcraft will explode if allowed to overheat. The redstone engine however can only overheat if not connected to anything at all.
Being connected even to a single wooden pipe (even if leading nowhere) will allow it to run indefinetly without any risk of exploding.
It will go from blue to green and then orange and when running at full power it will start blinking red-orange and will remain red-orange till swithched off or the load removed.
When in danger of exploding the engine will be fully red. They take a while to explode even when fully red.
The explosion of a overheated redstone engine is relatively weak, anything at more than 2 blocks from it is usually safe. Damage to the player is limited as well.