In the keel cooling system, the engine coolant is drawn by the engine water pump from the keel cooler mounted on the hull of the vessel and is forced through the engine oil cooler, cylinder block and head to the thermostat housing. Then it flows back to the keel cooler, completing its cooling circuit. A bypass from the thermostat housing to the inlet side of the water pump permits circulation of coolant through the engine when the thermostats are closed. When the thermostats open, the coolant flows into the surge tank and through the coils of the keel cooler to be cooled. See Figure 35476 .
The heat of the engine coolant is transferred through the keel cooler coils to the surrounding sea water.
Schematic of the Keel Cooling System (Raw Water Cooled)