Place stirling engine, add one piece of charcoal, power with redstone. Wait until charcoal is almost used up then it explodes.

They also continue generating energy when they don't have an active redstone signal, but I'm not sure if that's intentional.

Using Forge 10.13.1.1225 and a bunch of other mods including newest forestry unstable version and Railcraft.

The "also continue generating energy" is actually a rendering bug I am aware of. IIRC, they do not actually emit energy.

Engines are known to overheat if energy is not pulled away from them at an adequate rate. Does the engine get the usual green->orange->red cycling before exploding?

Nope. There is no color cycling, but it does happen if the engine is pumping to no energy output.

It doesn't emit energy, so that part's working.

Yeah, that mechanic makes sense, what doesn't make sense is how a single piece of charcoal is causing it when the engine isn't powered. I would have thought the engines were a bit more resistant to heat than that :P

Edit: And it doesn't color cycle, it just explodes out of the blue.

Here are some images of the setup:

I can see. I found that there are multiple bugs here:
a) the heat system is utterly and completely broken (fixing now),
b) the output estimate for certain engines is broken (fixing next),
c) the maximum energy storage values must be re-evaluated (fixing last).

👍 Awesome. I'm glad that RF Buildcraft is finally seeing the light of day :D Best of luck!

Thanks for the kind words.