Technical data

SECTION R
COOLING SYSTEM (EXTERNAL)
1. DESCRIPTION
Westerbeke marine diesel engines are equipped with fresh water cooling. Transfer of heat from engine
fresh water to sea water is accomplished by a heat exchanger, similar in function to an automotive
radiator. Sea water flows through the tubes of the heat exchanger while fresh water flows around the
tubes. The sea water and fresh water never mix with the result that the cooling water passages in the
engine stay clean.
2. FRESH WATER CIRCUIT
Heat rejected during combustion, as well as heat developed by friction, is absorbed by the fresh water
whose flow is created by a fresh water circulating pump. The fresh water flows from the engine through a
fresh water cooled exhaust manifold, a heat exchanger, in most cases an oil cooler, and returns to the
suction side of the fresh water circulating pump. The flow is not necessarily in this order in every model.
When starting a cold engine, most of the external flow to the heat exchanger is prevented by the closed
thermostat. Some amount of by-pass is maintained to prevent overheating in the exhaust manifold. As the
engine warms up, the thermostat begins to open up allowing full flow of engine fresh water through the
external cooling system.
3. SEA WATER CIRCUIT
The sea water flow is created by a positive displacement neoprene impeller pump (gear pump in
certain special cases). Normally the pump draws sea water directly from the ocean via the sea cock and
sea water strainer. Sometimes a transmission oil cooler, or perhaps a V-drive, will be piped on the
suction side of the sea water pump. Generally, it is better to have as few devices on the suction side of
the sea water pump as possible to preclude priming difficulties. Usually sea water flows directly from the
discharge of the sea water pump to the heat exchanger sea water inlet. After passing through the tubes of
the heat exchanger, the sea water may enter a transmission oil cooler, if present and if sea water cooled.
Ultimately, the sea water enters a water injected, wet exhaust system, the most popular type of exhaust
system in use. In the case of larger engines the sea water flow is divided prior to entering the exhaust
systems so that a portion is used to cool the exhaust system. Full sea water flow would create
unnecessary exhaust back pressure.
4. SEA WATER PUMP
The sea water pump is self priming and positive displacement. It is a rotary pump with a non-ferrous
housing and a neoprene impeller. The impeller has flexible vanes which wipe against a curved cam plate
within the impeller housing, producing the pumping action. On no account should this pump be run dry.
There should always be a spare impeller and impeller cover gasket aboard.