3304 & 3306 – Heat Exchanger Cooling System (Sea Water Aftercooled – SWAC)

This cooling system has two cooling circuits. One of these circuits is the engine coolant (jacket water) circuit. Normally this circuit cools the engine and attachments. The other circuit is the sea water circuit. In this system the sea water cools the aftercooler before it goes to heat exchanger (1) in expansion tank (2). In expansion tank (2), heat exchanger (1) cools the coolant from the engine coolant (jacket water) circuit.

Sea Water Circuit
The sea water comes in through inlet (30). Sea water pump (21) is driven by the timing gears. The location of sea water pump (21) is on the left front side of the engine below engine oil cooler (22). Rotation of the impeller pushes the sea water through aftercooler inlet line (13) to the rear of the engine. Aftercooler inlet line (13) connects to the aftercooler core. The core of the aftercooler is a group of tubes. These tubes are in a position inside aftercooler housing (12). The sea water goes through the tubes. The inlet air for the engine goes around the tubes. This cools the inlet air for the engine. The sea water comes out at the front of the engine. The sea water goes through aftercooler outlet line (8) to heat exchanger (1). Inside heat exchanger (1), the sea water goes through the tubes. The engine coolant (jacket water) goes through expansion tank (2) around the tubes of heat exchanger (1). This cools the engine coolant (jacket water). The sea water comes out of heat exchanger (1) through outlet line (17). Outlet line (17) sends the sea water through the outlet for sea water circuit (25).

This system can have duplex strainer (29) installed as shown. Duplex strainer (29) has two sides. Each side has a strainer which is large enough for the full flow of the sea water circuit. When the pressure drop across one of the strainers starts to get an increase, the full flow can be changed to the other strainer without stopping the engine.

Many cooling systems have a bypass valve (27) and a bypass line (26) installed as shown. Bypass valve (27) can be manually adjusted or automatically adjusted. Both kinds of valves have the same function. They work to control the minimum temperature of the sea water which goes through the aftercooler. The sea water going through outlet line (17) is hot. Bypass valve (27) controls the amount of the hot sea water which goes through bypass line (26). The hot sea water from bypass line (26) mixes with the sea water from the inlet for sea water circuit (30) as it goes to the inlet line (28) of sea water pump (21). When bypass valve (27) is correctly adjusted, the temperature of the sea water going into the aftercooler is as cool as possible without having condensation inside the aftercooler. (Condensation is water which comes out of the air when the air comes in contact with a cool surface.) This adjustment gives the engine the coolest inlet air for use at maximum horsepower ratings.

Engine Coolant (Jacket Water) Circuit
Water pump (20) for this circuit is on the left front side of the engine. It is gear driven by the timing gears. Coolant from expansion tank (2) goes through inlet line (19) to the water pump inlet. The rotation of the impeller in water pump (20) pushes the coolant (jacket water) through the circuit.

The coolant flow from water pump (20) goes through engine oil cooler (22) and bonnet (24). Bonnet (24) is on the outlet side of engine oil cooler (22) and connects to the side of cylinder block (16). On engines with auxiliary oil cooler (23), a different bonnet (24) is on the outlet of engine oil cooler (22). This bonnet (24) sends the coolant into one side of auxiliary oil cooler (23). At the bottom the coolant flow turns and goes up the other side of auxiliary oil cooler (23) and into bonnet (24) again. Then bonnet (24) sends this flow into cylinder block (16).

On engines with a water cooled turbocharger (11) some of the coolant in bonnet (24) goes through turbocharger inlet line (14). This coolant goes in at the bottom of water cooled turbocharger (11). The coolant goes up through water cooled turbocharger (11) and out through outlet line (10). Outlet line (10) sends the coolant into water cooled manifold (9) at the rear of the engine. The coolant goes through water cooled manifold (9) to the front of the engine. At the front of the engine the coolant comes out through outlet line (6) and goes into regulator housing (7). Inside regulator housing (7) the coolant mixes with the remainder of the coolant in cylinder head (15).

Inside cylinder block (16) the coolant goes around the cylinder lines and up through the water directors into cylinder head (15). The water directors send the flow of coolant around the valves and the passages for exhaust gases in cylinder head (15). The coolant goes to the front of cylinder head (15). Here the water temperature regulator controls the direction of the flow. If the coolant temperature is less than normal for engine operation, the water temperature regulator is closed. The only way for the coolant to get out of cylinder head (15) is through internal bypass (shunt) line (18). The coolant from this line goes into water pump (20) which pushes it through the cooling system again. The coolant from internal bypass (shunt) line (18) also works to prevent cavitation (air bubbles in the coolant). When the coolant gets to the correct temperature, the water temperature regulator opens and coolant flow is divided. Some goes through expansion tank (2) and around heat exchanger (1) for cooling. The rest goes through internal bypass (shunt) line (18) to water pump (20). The proportion of the two flows is controlled by the water temperature regulator.

NOTE: The water temperature regulator is an important part of the cooling system. It divides the coolant flow between heat exchanger (1) and internal bypass (18), as necessary, to maintain the correct operating temperature. If the regulator is not installed, there is no mechanical control, and most of the coolant will take the path of least resistance thru internal bypass line (18). This will cause the engine to overheat in hot weather. In cold weather, even the small amount of coolant that goes thru heat exchanger (1) is too much, and the engine will not get up to normal operating temperature.

Internal bypass (shunt) line (18) has another function when the cooling system is being filled. It lets the coolant go into cylinder head (15) and cylinder block (16) without going through water pump (20).

The coolant flow from the engine goes through outlet line (5) to expansion tank (2) and heat exchanger (1). Heat exchanger (1) is cooled by sea water from sea water pump (21) through aftercooler (12) and inlet line (28). The sea water cools the engine coolant (jacket water) in expansion tank (2) and goes out through sea water outlet (25).

Expansion tank (2) is the reservoir for the cooling system. It is the highest place in the cooling system. It is the place where the volume of the coolant can change because of heating or cooling without causing too much or too little coolant for the cooling system. Expansion tank (2) has a pressure cap (3) to control the pressure in the cooling system for better operation.

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