This is trivial but haven't found it on the forum. It would be nice if we could make thick armour on radiators side while keeping the surface armour lighter (nose-forward ships would warmly appreciate).
Also why do they stop glowing if they take a shot, even if they are not destroyed? And it seems that they keep the same color notwithstanding if the associated module (the one that need cooling) is used or not and how many there are of them (remaining, if some get shot).
The reason to turn off the radiator when it got shot is that if you continue turning it on, more coolant will be lost into the space.
Idk about the instant cooling though.
Depending on the material, and how well it radiates heat, it's entirely possible for a radiator to stop glowing once it's been shot and leaking. If the material doesn't radiate heat very well (why would you be using it for a radiator?) it does actually end up glowing for quite some time.