How does the temperature overlay work

kerbal-space-program

I've read about the temperature overlay in Kerbal Space Program here. And I've seen it, but how does it work?

When I turned it on f11, everything was red, which seems bad.

I've seen the temperature gauges come up during re-entry, which makes sense.

Kerbal Space Program re-entry heating overlay

Also, I've seen it come up with temperature gauges while flying in space with engines that weren't overheating (according to the staging list on the left). Why was that?

There's nothing in the tutorials or online. What is going on with the temperature gauges and heating overlay?

Best Answer

Colors start as red being cold, and goes red->orange->yellow gradually.

As for temp gauges showing up in space, that's because parts still get hot in space and cool down very slowly. An option here is to use radiators to quickly remove the heat. Other parts such as RTG's and batteries also overheat quickly and easily.

Temp gauges can also show up before the overheat bars on the staging area. Engine overheat bars show up at different temperatures for different engines.