Technically, nothing "prevents" the more modern units from getting hot and "overheating" in long tunnels. The computerized load control systems will begin to de-rate the horsepower, to prevent engine damage, but in reality, when the cooling water and lubricating oil reach the predetermined points of "excessive heat", the only corrective action is to reduce HP.

Dirty combustion air is a whole different situation, and once the prime mover (engine) begins choking on its own exhaust, then the result is drastic loss of HP.