3100 HEUI Diesel Truck Engine Cooling System

This engine has a pressure type cooling system with a shunt line.

A pressure type cooling system gives two advantages. The first advantage is that the cooling system can have a safe operation at a temperature that is higher than the normal boiling (steam) point of water. The second advantage is that this type of system prevents cavitation (the sudden making of low pressure bubbles in liquids by mechanical forces) in the water pump. With a pressure system, it is more difficult for an air or steam pocket to be made in the cooling system.

The shunt line keeps the water pump from cavitation, by providing a constant flow of coolant to the water pump.

NOTE: In air-to-air aftercooled systems, a coolant mixture with a minimum of 30 percent ethylene glycol base antifreeze must be used for efficient water pump performance. This mixture keeps the cavitation temperature range of the coolant high enough for efficient performance. Dowtherm 209 antifreeze can not be used because it does not raise the water pump cavitation temperature of the coolant high enough.

Cooling System Schematic
(1) Cylinder head. (2) Water temperature regulator housing. (3) Expansion tank. (4) Shunt line (expansion tank to water pump). (5) Bypass hose. (6) Radiator. (7) Cylinder block. (8) Oil cooler. (9) Water pump.

Water pump (9) is located on the right side of the cylinder block. It is belt driven from the crankshaft pulley. Coolant can enter the water pump three ways: through the bottom inlet of the water pump, through bypass hose (5) into the top of the water pump, or through shunt line (4) into the top of the water pump.

Coolant 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 enters the internal water manifold of the cylinder block. The manifold distributes the coolant to water jackets around the cylinder walls.


Water Lines Group
(1) Cylinder head. (2) Water temperature regulator housing. (5) Bypass hose. (10) Outlet (to radiator). (11) Water temperature regulator. (12) Air vent valve (located in flange of thermostat). (13) Water return from air compressor (if equipped). (14) Water temperature sensor. (15) Heater supply and return ports (located on the back side of housing).

From the cylinder block, the coolant flows into passages in the cylinder head. The passages send the flow around the unit injector sleeves and inlet and exhaust passages. The coolant now enters water temperature regulator housing (2) at the front right side of the cylinder head.

Water temperature regulator (11) controls the direction of flow. If the coolant temperature is less than normal, the water temperature regulator is closed. The coolant is directed through bypass hose (5) and into the top inlet of the water pump. When the coolant gets to the correct temperature, water temperature regulator (11) opens, and closes the bypass going to the pump. Most of the coolant goes through outlet (10) to the radiator for cooling. The remainder flows through bypass hose (5) and into the water pump.

The shunt line (4) runs from the top of the water pump to an expansion tank. This line must be routed to avoid trapping any air. By providing a constant flow of coolant available to the water pump, the shunt line keeps the water pump from cavitation.

NOTE: Water temperature regulator (11) is an important part of the cooling system. It divides coolant flow between the radiator and the bypass as necessary 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. In cold weather, even the small amount of coolant that goes through the radiator is too much, and the engine will not get to normal operating temperatures.

NOTE: Air vent valve (12) will allow the air to escape past the water temperature regulator from the cooling system while the radiator is being filled. During normal operation the air vent valve will be closed to prevent any coolant flow past the water temperature regulator.

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