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COOLING SYSTEM
Description
Westerbeke marine diesel engines are designed and equipped for fresh water cooling. Heat produced in
lbe engine by combustion and friction is transferred to fresh water which circulates lbroughout lbe engine
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
automotive radiator. Sea water flows through the tubes of the heat exchanger while fresh water flows
around lbe tubes; engine heat transferred to the fresh water is conducted lbrough the tube walls to lbe sea
water which is lben pumped into the exhaust system where finally it 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
lbe 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
NOTE: Refer to paragraphs A and B in this section on the recommended ethylene glycol antifreeze and
water mi,,1ure to be used as the fresh water coolant, and for information on filling the fresh water system.
Fresh water is pumped through lbe engine by a belt-driven circulating pump, absorbing heat from lbe
engine. The fresh water coolant circulates lbrough the engine's block absorbing heat, then passes Jbrough
lbe lbermostat into the exhaust manifold, to lbe heat exchanger where it is cooled, and then is returned to
lbe engine block through the suction side of the fresh
water circulating pump. When the engine is starred cold, external fresh water flow is prevented by lbe
closed lbermostat (allbough some fresh water flow is bypassed around lbe thermostat to prevent exhaust
manifold from overheating). As lbe engine warms up, the thermostat gradually opens, allowing full flow
of the engine's fresh water coolant to flow unrestricted to the e,,1ernal porrion of the cooling system.
A. Fresh Water Coolant (Antifreeze) Mixture.
A freshwater and ethylene glycol antifreeze mixture should be used year-round. Water, when it freezes,
expands sufficiently to split the heat exchanger and crack the engine block. A water/antifreeze mixture of
proper concentration will prevent freezing, reduce boil over and provide corrosion protection. Use soft
water "ith few impurities, such as tap water (potable water) or rainwater. Never use hard or foul water.
Use of hard 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 of poor quality or without
proper inhibitors
''''ill
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 of antifreeze. Make sure the engine's cooling system is well cleaned before adding
antifreeze. Recommended antifreeze 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
adding it to the cooling system.
ANTIFREEZE CONCENTRATION DATA
Antifreeze
Concentration
%
13
23
30
35
45
50
60
OF
23
14
5
-4
-22
-40
-58
Freezing
Temperature
eC)
( -5)
(-10)
(-15)
(-20)
(-30)
(-40)
(-50)
- -
A )0/)0 ethylene glycol mIxture IS recommended for year round use even
III
southern areas. MIxtures
below 30% or above 65% are not recommended.
62
Westerbeke Diesel Engines
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