3B7-77434-1 Tohatsu FILTER

Illustration 1 g00918015
Schematic of the cooling system for a power module
Jacket Water
Coolant flows from the radiator to the jacket water pump that is driven by the engine. Coolant flows from the pump into an adapter. The coolant is divided at the adapter. Part of the coolant is sent to the first stage of the aftercooler. Part of the coolant is sent to the front of the cylinder block. The other part of the coolant is sent through the engine oil cooler. The coolant flows from the engine oil cooler to the rear of the cylinder block.Coolant flows through the first stage of the aftercooler. The coolant then flows into the water jacket of the cylinder block. The coolant flows to both sides of the block through the distribution manifolds. The distribution manifolds are connected to the water jacket of all the cylinders. The main distribution manifold is located just above the main bearing oil gallery.The coolant flows upward through the cylinder water jacket. The coolant flows around the cylinder liners from the bottom to the top. Near the top of the cylinder liners, the water jacket is made smaller. This is the area that has the hottest temperature. This shelf (smaller area) causes the coolant to flow faster for better liner cooling. Coolant from the top of the liners flows into the cylinder head which sends the coolant around the parts that have the hottest temperature. Coolant flows to the top of the cylinder head (one at each cylinder). The coolant flows out of the cylinder head through an elbow into a water manifold. Coolant then flows through the manifold to the temperature regulator housing.The regulator housing has an upper flow section and a lower flow section. The regulator housing contains four temperature regulators. The sensing bulbs of the four temperature regulators are in the coolant in the lower section of the housing. Before the regulators open, cold coolant is sent through the bypass line back to the inlet of the water pump. As the temperature of the coolant increases, the regulators start to open. The regulators restrict the flow of coolant in the bypass line. Some of the coolant is sent to the radiator for cooling.Coolant for the water cooled turbochargers is picked up from the rear of the water manifold. The coolant flows through the water cooled turbochargers and the coolant returns to the engine block.Separate Circuit Aftercooler (SCAC)
The second stage of the aftercooler uses a separate circuit. Coolant flows from the radiator to an auxiliary water pump that is driven by the engine. The auxiliary water pump sends the coolant to the second stage of the aftercooler. The coolant flows through the second stage of the aftercooler to a thermostatic valve.When the coolant is below operating temperature, the thermostatic valve is closed. This will bypass the radiator. The coolant is returned to the auxiliary water pump. When the coolant in the separate circuit is up to operating temperature, the thermostatic valve opens. This will allow the coolant to flow from the core of the aftercooler to the radiator. The water flows through the radiator and returns to the auxiliary water pump.