Cooling System - Westerbeke 9.0 BCG Technical Manual

COOLING SYSTEM
Description
Westerbeke marine gasoline engines are designed and equipped for fresh water cooling. Heat produced in
the engine by combustion and friction is transferred to the fresh water which circulates throughout the en-
gine. This circulating fresh water cools the engine block and its internal moving parts. The heat is transferred
externally from the fresh water to sea water by means of a heat exchanger, similar in function to an automo-
tive radiator. Sea water flows through the tubes of the heat exchanger while fresh water flows around the
tubes; engine heat transferred to fresh water is conducted through the tube walls to the sea water which is
pumped into the exhaust system and discharged overboard. In basic terms, the engine is cooled by fresh
water, the fresh water is cooled by sea water, and the sea water carries the transferred heat over the side
through the exhaust system. The fresh water and sea water circuits are independent of each other. Using
only fresh water within the engine allows the cooling water passages to stay clean and free from harmful
deposits. The two independent circuits and their components are discussed in the following paragraphs.
Fresh Water Circuit
Fresh water is pumped through the engine by a belt-driven circulating pump, absorbing heat created by in-
ternal combustion and by friction. The fresh water coolant circulates throughout the engine block absorb-
ing heat, then passes through the thermostat into the exhaust manifold, then to the heat exchanger where
it is cooled, and then is returned to the engine block through the suction side of the fresh water circulating
pump. When the engine is started cold, external fresh water flow is prevented by the closed thermostat (al-
though some fresh water flow is bypassed around the thermostat to prevent the exhaust manifold from over-
heating). As the engine warms up, the thermostat gradually opens, allowing the engine's fresh water coolant
to flow unrestricted to the external portion of the cooling system.
Sea Water Circuit
The sea water flow is created by a positive displacement neoprene impeller pump. Normally the pump draws
sea water directly from the ocean through a flush-hull sea cock and sea water strainer. Sea water then flows
directly from the discharge of the sea water pump to the heat exchanger sea water inlet. Here it passes
through the tubes of the heat exchanger where it removes heat from the engine's fresh water cooling sys-
tem that is circulating around the outside of these tubes. The sea water then exits the exchanger and is
directed with wire reinforced hosing through a syphon break fitting, when needed, to the inlet of the water
injected exhaust elbow where it mixes with and cools the exhaust gases and then is passed through the ex-
haust system and discharged overboard.
Sea Water Pump
The sea water pump is self priming and positive displacement. This rotary sea water pump has a non-fer-
rous housing and a neoprene impeller. The impeller has flexible vanes which wipe against a curved cam
plate within the impeller housing, producing a pumping action. On no account should this pump be run
dry. There should always be a spare impeller and impeller cover gasket aboard (an impeller kit).
Westerbeke Generators
160