3B7-01291-1 Nissan LOWER HEAD, CRANK CASE

Raw Water Circuit
The auxiliary water pump that is used for the raw water circuit is located on the left hand side of the cylinder block. The water pump is driven by the front gear train.In many instances, a separate cooling source is used to supply coolant to the aftercooler. The coolant supply for this raw water circuit is sea water. A special pump is needed to move the coolant through the system. A bronze pump is used for a sea water cooling system. This type of pump will resist the corrosive action of the coolant that passes through the pump.Raw water is drawn in through the inlet of the auxiliary water pump. The raw water will flow through the fuel cooler before the auxiliary water pump inlet if the engine is equipped with the optional fuel cooler. The raw water is forced out of the pump and into the aftercooler. The raw water flows through the aftercooler and exits at the end of the aftercooler. The raw water then travels through the heat exchanger, and the water cooled exhaust elbow. The raw water is then discharged.Engine Coolant Flow Circuit
The water pump that is used for engine coolant is located on the right hand side of the cylinder block. The water pump is driven by the front gear train.Coolant from the heat exchanger is pulled into the inlet of the water pump by impeller rotation. The coolant exits the water pump and flows directly into the engine oil cooler.After the water exits the oil cooler, the water is dispersed to three main components: cylinder block and head, turbocharger and exhaust manifold.The coolant that was directed to the cylinder block next flows into the cylinder head.The coolant exits the cylinder head and combines with the flow of coolant from the exhaust manifold and the turbocharger. This combined coolant flows to the water temperature regulator. The coolant then flows through a deaerator in order to purge excess air to the expansion tank. The water is then returned to the heat exchanger in order to be cooled.Air vents are provided on the water outlet of the turbocharger. The air vents aid in removing air from the system during the initial filling of the cooling system. The air vents also aid in removing air from the system after a flushing process.Note: The water temperature regulator controls the direction of flow. When the coolant temperature is below the normal operating temperature, the water temperature regulator is closed. The coolant is directed from the cylinder head to the inlet of the water pump. When the coolant temperature reaches the normal operating temperature, the water temperature regulator opens. Coolant then travels to the heat exchanger for cooling.Note: The water temperature regulator is an important part of the cooling system. The water temperature regulator divides coolant flow between the heat exchanger and the bypass in order to maintain the normal operating temperature. If the water temperature regulator is not installed in the system, there is no mechanical control, and most of the coolant will travel the path of least resistance through the bypass. This will cause the engine to overheat in hot weather and the engine will not reach normal operating temperature in cold weather.Heat Exchangers
This engine is equipped with a raw water heat exchanger. This heat exchanger provides a system that will allow heat to be transferred from the engine cooling system to a separate circuit water system. The separate circuit water system that is used for this engine is the raw water circuit.Heat exchangers are typically designed as a shell that surrounds many thin tubes. Systems that are cooled with a heat exchanger require an auxiliary water pump in order to circulate raw water through the thin tubes in the heat exchanger. Cooling system water is then circulated in the opposite direction through the shell that surrounds the tubes. Heat is transferred from the hot coolant to the cool water that is flowing through the thin tubes.