Hello Mr. Tore,
When I look at Plan 13 the cooling water system, it looks like Cooling Water Out valves on the starboard side are always open to have the water flow through the e-motor coolers, bearings, thrust bearings and Junkers compressor. Then when the U-Boat dives, the valves are opened on the port side to provide the cooling water for the stern mechanisms, plus provide cooling water for the diesel engines towards the diesel room.
When running silent, would they ever shut off the cooling water pump?
Regards,
Don_