3A3-84401-0 Tohatsu NEUTRAL LOCK ARM

Illustration 1 g06241035
Cooling system schematic
(1) Cylinder head
(2) Water temperature regulator housing
(3) Expansion tank
(4) Shunt line (expansion tank to water pump)
(5) Bypass
(6) Radiator
(7) Cylinder block
(8) Oil cooler
(9) Water pumpWater pump (10) is on the right side of the cylinder block. The water pump is belt driven from the crankshaft pulley. Coolant can enter the water pump in three places:
Inlet at the bottom of the water pump
Bypass (6) into the top of the water pump
Shunt line (5) into the top of the water pumpCoolant from the bottom of the radiator is pulled into the bottom inlet of the pump by impeller rotation. The coolant exits the back of the pump directly into the oil cooler cavity of the block.All the coolant passes through the core of the oil cooler and the coolant enters the internal water manifold of the cylinder block. The manifold disperses the coolant to water jackets around the cylinder walls.From the cylinder block, the coolant flows into passages in the cylinder head. The passages send the flow around the unit injector sleeves and the inlet and the exhaust passages. The coolant now enters water temperature regulator housing (3) at the front right side.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 through bypass (6) and into the top inlet of the water pump. When the coolant temperature reaches the normal operating temperature, the water temperature regulator opens. When the water temperature regulator is open, the bypass is closed. Most of the coolant goes through the outlet to the radiator for cooling. The remainder flows through bypass (6) and into the water pump.The shunt line (5) extends from the top of the water pump to an expansion tank. The shunt line must be routed properly to avoid trapping any air. By providing a constant head pressure to the water pump, the shunt line can provide a constant flow of coolant to the water pump. This shunt line prevents cavitation by the water pump.Note: The water temperature regulator is an important part of the cooling system. The water temperature regulator divides coolant flow between the radiator and the bypass to maintain the normal operating temperature. If the water temperature regulator is not installed, there is no mechanical control, and most of the coolant will travel the path of least resistance. The path of least resistance is through the bypass. Also, the lack of control will cause the engine to overheat in hot weather and not reach normal operating temperature in cold weather.Coolant For Air Compressor (If Equipped)
If the engine is equipped with an air compressor, the air compressor coolant is supplied from the water temperature regulator housing through the supply line. The coolant is circulated through the air compressor and is returned to the cooling system through the return line into the cylinder head.Coolant Conditioner (If Equipped)
Some conditions of operation can cause pitting. 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 like the fuel filter and the oil filter elements. The coolant conditioner element attaches to the coolant conditioner base that is mounted on the front of the engine. Coolant flows from the water pump to the coolant conditioner base and back to the cylinder block. Coolant constantly flows through the coolant conditioner element when the valves are in the OPEN position.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 to get the necessary concentration for cooling system protection. The elements also contain a filter. The coolant conditioner elements should remain in the system after the conditioner material has dissolved. The precharge element contains 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 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. Enough of inhibitor is provided by the maintenance elements to maintain the corrosion protection at an acceptable level. After the first change interval, only maintenance elements are installed. To provide the cooling system with protection, maintenance elements are installed at specific intervals.