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COOLING SYSTEM
Description
Westerbeke marine diesel engines are designed and equipped for fresh water cooling. Heat produced in the
engine by combustion and friction is transferred to fresh water which circulates throughout the engine. This
circulating fresh water cools the engine block and its internal moving parts. The heat is transferred external-
ly from the fresh water to sea water by means of 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;
engine heat transferred to the fresh water is conducted through the tube walls to the sea water which is then
pumped into the exhaust system where finally itis discharged overboard. In other words, 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 harm-
ful deposits. The two independent circuits and their components are discussed in the following paragraphs.
Fresh Water Circuit
NOTE: Refer to paragraphs A and B in this section for the recommended antifreeze and water
mixture to be used as the fresh water coolant, and for information on filling the fresh water sys-
tem.
Fresh water is pumped through the engine by a belt-driven Circulating pump, absorbing heat from the en-
gine. The fresh water coolant circulates through the engine's block absorbing heat, then passes through the
thermostat into the exhaust manifold, 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 (although some fresh water flow is bypassed
around the thermostat to prevent exhaust manifold from overheating). As the engine warms up, the thermo-
stat gradually opens, allowing full flow of the engine's fresh water coolant to flow unrestricted to the external
portion of the cooling system.
A. Fresh Water Coolant (Antifreeze) Mixture.
It is recommended that a freshwater and antifreeze mixture be used year-round. Water, when it freezes, ex-
pands sufficiently to split the heat exchanger and crack the engine block. A water/antifreeze mixture of proper
concentration will prevent freezing (see page 40 for an antifreeze/water mixture chart).
Use soft water with few impurities, such as tap water (potable water) or rainwater. Never use hard or foul
water. Use of hard water or water containing impurities will lead to the collection of scale in the engine and
heat exchanger which will reduce the cooling system's efficiency.
Antifreeze
01
poor quality or without rust inhibitors will cause corrosion within the cooling system. Always
use antifreeze which is compatible with aluminum cooling system components and is made by a reliable
manufacturer. Never mix different brands
01
antifreeze.
Make sure that the cooling system of the engine is well cleaned before adding antifreeze. Recommended an-
tifreeze for year round use is ZEREX or PRESTONE with rust inhibitors.
In order to control the concentration of the mixture, mix the antifreeze and freshwater thoroughly before ad·
ding it to the cooling system.
39
Weslerbeke Diesel Engines
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