3304 & 3306 – Keel Cooling System (Engines Without Aftercooler)


COOLANT FLOW FOR KEEL COOLING SYSTEM
1. Expansion tank. 2. Pressure cap. 3. Inlet line. 4. Internal bypass (shunt) line. 5. Water cooled manifold or water cooled shield for manifold. 6. Outlet line. 7. Block. 8. Water cooled shield for turbocharger. 9. Line to keel cooler. 10. Cylinder head. 11. Cylinder block. 12. Return line from keel cooler. 13. Supply line for water pump. 14. Keel cooler tubes. 15. Water pump. 16. Engine oil cooler. 17. Oil cooler for torque converter or marine gear. 18. Bonnet. 19. Return line.

The water pump (15) is on the left front side of the engine. It is gear driven by the timing gears. Coolant from the bottom of the expansion tank (1) goes to the water pump inlet. The rotation of the impeller in the water pump (15) pushes the coolant through the system.

All of the coolant flow from the water pump (15) in the standard system, goes through the engine oil cooler (16). The bonnet (18) on the outlet side of the engine oil cooler (16) connects to the side of the cylinder block (11).

On engines with an additional oil cooler (17), a different bonnet (18) is on the engine oil cooler (16). This bonnet (18) sends the coolant flow through the other oil cooler which is for attachments such as torque converters or marine gears. The flow goes through one side on the way into the cooler. At the bottom of the cooler the flow turns and goes back up through the other side and into the bonnet (18) again. The bonnet (18) sends the coolant into the cylinder block (11).

An engine can have a water cooled manifold or a water cooled shield for the manifold (5). If it has either one of these it can also have a water cooled shield for the turbocharger (8). The coolant flow from the water pump (15) is divided. Some of the coolant goes through the standard system and some goes into the water cooled manifold or water cooled shield for the manifold (5) at the front of the engine. It comes out at the rear of the engine and goes through a return line (19) to the bonnet (18) on the engine oil cooler (16). It mixes with the rest of the coolant from the standard system in the bonnet (18) and goes into the cylinder block (11).

If the engine has a water cooled shield for the turbocharger (8), the supply of coolant for it comes from the bottom of the rear end of the water cooled manifold or water cooled shield for the manifold (5). The coolant goes through the water cooled shield for the turbocharger (8). It goes out through outlet line (6) to block (7) at the top of the water cooled manifold or water cooled shield for the manifold (5). In the block (7) it mixes with the rest of the coolant on the way to the bonnet (18).

Inside the cylinder block (11) the coolant goes around the cylinder liners and up through the water directors into the cylinder head (10). The water directors send the flow of coolant around the valves and the passages for exhaust gases in the cylinder head (10). The coolant goes to the front of the cylinder head (10). 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 the cylinder head (10) is through the internal bypass (shunt) line (4). The coolant from this line goes into the water pump (15) which pushes it through the cooling system again. The coolant from the internal bypass (shunt) line (4) 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 the keel cooler tubes (14) for cooling. The rest goes through the internal bypass (shunt) line (4) to the water pump (15). 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 (14) and internal bypass (4), 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 (4). 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 (14) is too much, and the engine will not get up to normal operating temperature.

The internal bypass (shunt) line (4) has another function when the cooling system is being filled. It lets the coolant go into the cylinder head (10) and cylinder block (11) without going through the water pump (15).

The keel cooler tubes (14) 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 the keel cooler tubes (14) the rate at which sea water goes around the outside of the keel cooler tubes (14), the temperature of the sea water, and the rate of flow of the engine coolant through the keel cooler tubes (14).

After going through the keel cooler tubes (14) the coolant goes to an expansion tank (1). The expansion tank (1) is a reservoir for the coolant. 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. The expansion tank (1) has a pressure cap (2) to control the pressure in the cooling system for better operation.

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