The term 'jacket water', in Diesels at least, usually refers to a glycol/water loop that's usually closed, pressurized and thermostatically regulated to 160F or thereabouts.
That loop is typically cooled by:
radiators, or
heat exchangers and seawater, or
heat exchangers and a cooling tower loop with freshwater makeup
Engine manufacturers often >>strongly suggest<< the use of sizable air separators in the liquid circuits, just to make sure that the pumps are pumping liquid, etc.
Mike Halloran
Pembroke Pines, FL, USA