3304 & 3306 – Keel Cooling System (Separate Circuit Aftercooled)


COOLING SYSTEM SCHEMATIC
1. Outlet line. 2. Expansion tank. 3. Pressure cap. 4. Cylinder block. 5. Cylinder head. 6. Water cooled manifold. 7. Outlet line. 8. Regulator housing. 9. Outlet line. 10. Aftercooler housing. 11. Water cooled turbocharger. 12. Expansion tank. 13. Pressure cap. 14. Bypass filter. 15. Inlet line. 16. Duplex strainer. 17. Inlet line. 18. Bonnet. 19. Inlet line. 20. Inlet line. 21. Auxiliary pump. 22. Engine oil cooler. 23. Auxiliary oil cooler. 24. Duplex strainer. 25. Inlet line. 26. Keel cooler tubes. 27. Internal bypass (shunt) line. 28. Water pump. 29. Outlet line. 30. Bypass filter. 31. Bypass valve. 32. Bypass line. 33. Keel cooler tubes.

This cooling system has two completely separate cooling circuits. One of these circuits is the engine coolant (jacket water) circuit. Normally this circuit cools the engine and all the attachments. The other circuit is the aftercooler circuit. It normally cools the aftercooler only. This type of cooling system keeps the temperatures of the coolant in the two circuits in the correct ranges for the maximum horsepower output.

Aftercooler Circuit
The aftercooler circuit uses auxiliary pump (21). It is on the left front side of the engine below engine oil cooler (22). Auxiliary pump (21) is gear driven by the timing gears. Coolant from keel cooler tubes (33) goes to the inlet of auxiliary pump (21). The rotation of the impeller pushes the coolant through the aftercooler circuit.

All of the coolant flow goes through inlet line (19). Inlet line (19) connects to the aftercooler at the rear of the engine. The coolant goes through the core of the aftercooler to the front of the engine. The core of the aftercooler is a group of tubes. These tubes are in position inside aftercooler housing (10). The coolant goes through the tubes. The inlet air for the engine goes around the tubes. This cools the inlet air. The coolant comes out of the cover of the aftercooler at the front of the engine and into outlet line (29). Outlet line (29) connects to keel cooler tubes (33).

Keel cooler tubes (33) are normally installed on the bottom of the hull in front of the keel cooler tubes for the engine coolant (jacket water) circuit. This position gives the maximum cooling. Keel cooler tubes (33) are usually made of a metal which has resistance to corrosion because they give off heat from the coolant to the sea water which the hull is in. The efficiency of this action is in relation to: the surface area of keel cooler tubes (33), the rate at which sea water goes around the outside of the keel cooler tubes (33), the temperature of the sea water, and the rate of flow of the coolant through keel cooler tubes (33).

After going through keel cooler tubes (33), the coolant goes to the inlet for auxiliary pump (21). An expansion tank (12) is connected to inlet line (25). Expansion tank (12) has the necessary room for the coolant when it expands (uses more space) from being heated.

This system can have duplex strainer (24) installed in the line from keel cooler tubes (33). Duplex strainer (24) has two sides. Each side has a strainer which is large enough for the full flow of the cooling system. 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.

Some cooling systems have a bypass filter (30). This is installed between the inlet and outlet lines for keel cooler tubes (33). In this position, a small part of the coolant flow goes through bypass filter (30). This flow removes the particles which are too small for removal by duplex strainer (24).

Many cooling systems have a bypass valve (31) and bypass line (32) installed as shown. The bypass valve can be either manually adjusted or automatically adjusted. Both kinds of valves have the same function. They control the minimum temperature of the coolant which goes to the aftercooler. Bypass valve (31) controls the temperature of the coolant by controlling the amount of coolant which can go through the bypass line (32) instead of through keel cooler tubes (33). The coolant which goes through bypass line (32) is hot. It mixes with the coolant from keel cooler tubes (33) as it goes to the inlet for auxiliary pump (21). When bypass valve (32) is correctly adjusted, the coolant temperature 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 (28) for this circuit is on the left front side of the engine. It is gear driven by the timing gears. Coolant from the bottom of expansion tank (2) goes to the water pump inlet. The rotation of the impeller in water pump (28) pushes the coolant through the circuit.

All of the coolant flow from water pump (28) in this circuit, goes through engine oil cooler (22). Bonnet (18) on the outlet side of engine oil cooler (22) connects to the side of cylinder block (4).

On engines with an auxiliary oil cooler (23), a different bonnet (18) is on the engine oil cooler (22). This bonnet (18) sends the coolant flow through auxiliary oil cooler (23) which is for attachments such as torque converters or marine gears. The flow goes through one side on the way in.

At the bottom of auxiliary oil cooler (23) the flow turns and goes back up through the other side and into bonnet (18) again. Bonnet (18) sends the coolant into cylinder block (4).

Some of the coolant which goes through bonnet (18) is sent through inlet line (20) to the bottom of the water cooled turbocharger (11) at the rear of the engine. This coolant goes up through the water cooled turbocharger and out at the top through outlet line (9). Outlet line (9) connects to the top of water cooled manifold (6) near the rear of the engine. The coolant goes through water cooled manifold (6) to the front of the engine. At the front of the engine, the coolant goes through outlet line (7) and into regulator housing (8) where the coolant mixes with the coolant from cylinder head (5).

Inside cylinder block (4) the coolant goes around the cylinder liners and up through the water directors into cylinder head (5). The water directors send the flow of coolant around the valves and the passages for exhaust gases in cylinder head (5). The coolant goes to the front of cylinder head (5). 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 (5) is through internal bypass (shunt) line (27). The coolant from this line goes into water pump (28) which pushes it through the cooling system again. The coolant from internal bypass (shunt) line (27) also works to prevent cavitation (air bubbles in the coolant). When the coolant gets to the correct temperature, the water temperature regulator opens and the coolant flow is divided. Some goes through keel cooler tubes (26) for cooling. The rest goes through internal bypass (shunt) line (27) to water pump (28). 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 keel cooler tubes (26) and internal bypass (27), 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 (27). This will cause the engine to overheat in hot weather. In cold weather, even the small amount of coolant that goes thru the keel cooler tubes (26) is too much, and the engine will not get up to normal operating temperature.

Internal bypass (shunt) line (27) has another function when the cooling system is being filled. It lets the coolant go into cylinder head (5) and cylinder block (4) without going through water pump (28).

Keel cooler tubes (26) are normally installed on the bottom of the hull. They are usually made of a metal which has resistance to corrosion because they give off heat from the engine coolant to the sea water which the hull is in. The efficiency of this action is in relation to: the surface area of keel cooler tubes (26), the rate at which sea water goes around the outside of keel cooler tubes (26), the temperature of the sea water, and the rate of flow of the engine coolant through keel cooler tubes (26).

After going through keel cooler tubes (26), the coolant goes to an expansion tank (2). Expansion tank (2) is a reservoir for the coolant. It is the highest place in the cooling circuit. 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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