3304 & 3306 – Heat Exchanger Cooling System (Jacket Water Aftercooled – JWAC)

1. Heat exchanger. 2. Expansion tank. 3. Pressure cap. 4. Vent line. 5. Outlet line. 6. Outlet line. 7. Regulator housing. 8. Aftercooler inlet line. 9. Water cooled manifold. 10. Outlet line. 11. Water cooled turbocharger. 12. Aftercooler housing. 13. Cylinder head. 14. Aftercooler outlet line. 15. Internal bypass (shunt) line. 16. Turbocharger inlet line. 17. Cylinder block. 18. Outlet line. 19. Bonnet. 20. Inlet line. 21. Inlet line. 22. Water pump. 23. Sea water pump. 24. Engine oil cooler. 25. Auxiliary oil cooler. 26. Outlet for sea water circuit. 27. Bypass valve. 28. Bypass line. 29. Duplex strainer. 30. Inlet for sea water circuit.

This cooling system has two circuits which work together. The engine coolant (jacket water) circuit cools the aftercooler, the engine and the auxiliary oil cooler. The coolant from this circuit can go through expansion tank (2). In expansion tank (2) this coolant goes around the tubes of heat exchanger (1) while the coolant from the sea water circuit goes through the tubes. In this way the sea water cools the engine coolant (jacket water). The sea water goes through heat exchanger (1) when the engine is running. The engine coolant (jacket water) only goes through expansion tank (2) and around the tubes of heat exchanger (1) when the water temperature regulator in the engine is open.

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 (23) is on the left front side of the engine below engine oil cooler (24). Rotation of the impeller pushes the sea water through inlet line (21) to heat exchanger (1). In heat exchanger (1) the sea water goes through the tubes and out through outlet line (18) and outlet (26). The engine coolant (jacket water) goes through expansion tank (2) and around the tubes of heat exchanger (1). This cools the engine coolant (jacket water).

Engine Coolant (Jacket Water) Circuit
Water pump (22) 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 (20) to the water pump inlet. The rotation of the impeller in water pump (22) pushes the coolant (jacket water) through the circuit.

The coolant flow from water pump (22) is divided. Some of the coolant flow goes through engine oil cooler (24). The remainder of the coolant flow goes through aftercooler inlet line (8) into the core of the aftercooler. The core of the aftercooler is a group of tubes. These tubes are in a position inside aftercooler housing (12). The coolant goes through the tubes. This inlet air for the engine goes around the tubes. This cools the inlet air. The coolant comes out at the rear of the engine and goes through aftercooler outlet line (14) to bonnet (19). In bonnet (19) the coolant flow mixes with the coolant flow from engine oil cooler (24).

The coolant flow which comes through engine oil cooler (24) goes through bonnet (19). If the engine has a water cooled turbocharger (11), some of the coolant flow from engine oil cooler (24) goes through turbocharger inlet line (16). The coolant flow goes in at the bottom of water cooled turbocharger (11) and comes out at the top. It goes through outlet line (10) to the top of water cooled manifold (9). It goes through water cooled manifold (9) to the front of the engine. It comes out through outlet line (6) and goes into regulator housing (7). The coolant flow mixes with the rest of the coolant from the engine.

The remainder of coolant flow through bonnet (19) goes into one side of auxiliary oil cooler (25). At the bottom the coolant flow turns and goes up the other side of auxiliary oil cooler (25) and into bonnet (19) again. Bonnet (19) sends this flow into cylinder block (17).

Inside cylinder block (17) the coolant goes around the cylinder liners and up through the water directors into cylinder head (13). The water directors send the flow of coolant around the valves and the passages for exhaust gases in cylinder head (13). The coolant goes to the front of cylinder head (13). 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 (13) is through internal bypass (shunt) line (15). The coolant from this line goes into water pump (22) which pushes it through the cooling system again. The coolant from internal bypass (shunt) line (15) 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 (15) to water pump (22). 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 (15), 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 (15). 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 (15) has another function when the cooling system is being filled. It lets the coolant go into cylinder head (13) and cylinder block (17) without going through water pump (22).

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 sent by sea water pump (23) through inlet line (21). The sea water cools the engine coolant in expansion tank (2) and goes out through the outlet for sea water circuit (26).

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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