Coolant Circuit
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| Illustration 1 | g01029677 |
Cooling system schematic (typical example) (1) Turbocharger drain lines (2) Water cooled turbocharger housing (3) Aftercooler (4) Vent lines (5) Deaerator (6) Expansion tank (7) Raw water heat exchanger (8) Riser to water cooled manifold (9) Water pump inlet (10) Water cooled manifold (11) Tube from expansion tank to water pump (12) Jacket water pump (13) Manifold (14) Jacket water heater (15) Bonnet (16) Oil cooler | |
The 3408 and 3412 High Performance Marine Engines use a separate raw water pump, an integral surge tank, and a heat exchanger in order to provide a more compact engine installation. The jacket water cooling system is a pressure type cooling system. The system is designed with the following components that are water cooled:
- exhaust manifolds
- risers
- turbochargers
This pressure type cooling system can operate safely at a temperature that is higher than the normal boiling point (steam) of water. A pressure type cooling system also helps to prevent cavitation which can damage engine components. Cavitation is the sudden formation of low pressure bubbles that are caused by mechanical forces in liquids. An integral deaerator is built into the jacket water cooling system in order to remove air bubbles from the coolant. The formation of air or steam pockets is more difficult within a pressure type cooling system. The extensive use of water cooled manifolds helps to minimize excess heat that would be radiated into the engine room.
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| Illustration 2 | g01029686 |
(6) Expansion tank (7) Raw water heat exchanger (12) Jacket water pump (17) Raw water inlet (18) Raw water pump (19) Turbocharger supply from block | |
The jacket water pump (12) forces coolant into manifold (13). The coolant flow is then divided.
Part of the coolant from the water pump is sent to the aftercooler (3) in order to cool the inlet air for the engine. From the aftercooler core, the coolant then enters the cylinder block at the top rear of the engine. This flow is directed from the rear of the cylinder block into the rear of the cylinder heads toward the front of the engine. The coolant exits the cylinder heads at the front of the engine into the risers (8) through the water cooled manifolds (10) in the front of the cylinder heads. This coolant then combines with the coolant flow from the cylinder block and the cylinder heads.
Another part of the coolant flows through the engine oil cooler (16). After leaving the oil cooler, the flow is divided again at the bonnet of the oil cooler (15). A portion of the flow is redirected in order to cool the cylinder block, the cylinder liners, and the cylinder heads. After passing through the temperature regulators, the coolant is pumped through the bypass lines, or through the deaerators into the heat exchanger. The coolant then returns to the inlet of the water pump. The remaining flow is directed through lines (19) into the bottom of the turbocharger housing (2). The coolant then flows out of the top of the housing, into the turbocharger drain lines (1), into the risers (8), and through the exhaust manifolds (10). The flow moves from the exhaust manifold to the front of the cylinder head for return through the temperature regulators. Vent lines (4) connect the turbochargers, the deaerator and the expansion tank. A separate tube (11) connects the expansion tank directly with the water pump.
The raw water pump (auxiliary water pump) (18) supplies a continuous flow of raw water to the heat exchanger for cooling. Raw water is drawn in through the raw water inlet (17). This water is used in order to cool the jacket water. The water is then pumped through the outlet tube and into the marine gear cooler and the water cooled exhaust manifold.
Note: The water temperature regulator is an important part of the cooling system. The regulator divides coolant flow between the heat exchanger and the bypass lines in order to maintain the correct temperature. If the water temperature regulator is not installed in the system, there is no mechanical control, and most of the coolant will take the path of least resistance through the bypass. This will cause the engine to overheat in hot weather and the engine will not reach the normal operating temperature in cold weather. If this is allowed to happen, the engine may not reach operating temperatures.
When the engine is cold, the water temperature regulators are closed, and the coolant is stopped from flowing to the heat exchanger. The coolant flows from the temperature regulator housing back to the water pump through the bypass lines.
Coolant Conditioner
Some conditions of operation can cause pitting on the outer surface of the cylinder liners and on the cylinder block surface next to the liners. This pitting is caused by corrosion or by cavitation erosion. A corrosion inhibitor is a chemical that provides a reduction in pitting. The addition of a corrosion inhibitor can keep this type of damage to a minimum.
The coolant conditioner element is a spin-on element that is similar to a fuel filter and to oil filter elements. The coolant conditioner element attaches to the coolant conditioner base that is mounted on the engine or mounted on a remote location. Coolant flows through lines from the water pump to the base and back to the block. There is a constant flow of coolant through the element.
The element has a specific amount of inhibitor for acceptable cooling system protection. As the coolant flows through the element, the corrosion inhibitor goes into the solution. The corrosion inhibitor is a dry solution, so the inhibitor dissolves. The corrosion inhibitor then mixes to the correct concentration. Two basic types of elements are used for the cooling system. The two elements are the precharge elements and the maintenance elements. Each type of element has a specific use. The elements must be used correctly in order to get the necessary concentration for cooling system protection. The elements also contain a filter. The elements should remain in the system after the conditioner material is dissolved.
The precharge elements contain more than the normal amount of inhibitor. The precharge element is used when a system is first filled with new coolant. This element must add enough inhibitor in order to bring the complete cooling system up to the correct concentration.
The maintenance elements have a normal amount of inhibitor. The maintenance elements are installed at the first change interval. A sufficient amount of inhibitor is provided by the maintenance elements in order to maintain the corrosion protection at an acceptable level. After the first change interval, only maintenance elements are installed. In order to provide the cooling system with protection, maintenance elements are installed at specific intervals.