C9 Industrial Engines Cooling System Caterpillar


Cooling System
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1.1. Coolant For Air Compressor (If Equipped)
2.1. Coolant Conditioner (If Equipped)

This engine has a pressure type cooling system that is equipped with a shunt line (9).

A pressure type cooling system offers two advantages:

  • The cooling system can operate safely at a temperature that is higher than the normal boiling point of water.

  • The cooling system prevents cavitation in the water pump.

Cavitation is the sudden formation of low pressure bubbles in liquids by mechanical forces. The formation of air or steam pockets is more difficult within a pressure type cooling system.

The shunt line (9) prevents cavitation by the water pump. The shunt line (9) provides 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. Refer to Operation and Maintenance Manual, "Refill Capacities and Recommendations" for more information on the recommended coolant mixtures.



Illustration 1g01123296
(1) Cylinder head
(2) Water temperature regulator housing
(3) Expansion tank
(4) Bypass hose
(5) Cylinder block
(6) Oil cooler
(7) Water pump
(8) Radiator
(9) Shunt line

Water pump (7) is located on the right side of the cylinder block. The water pump is driven by a belt that is powered by the crankshaft pulley. Coolant can enter the water pump in three places:

  • Inlet at the bottom of the water pump

  • Bypass hose (4) which is located on the top of the water pump

  • Shunt line

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 of 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.



Illustration 2g01123308


Illustration 3g01121591
(7) Water pump
(10) Bypass inlet


Illustration 4g01123344
Single water temperature regulator housing
(1) Cylinder head
(2) Water temperature regulator housing
(4) Bypass hose
(11) Water temperature regulator


Illustration 5g01123311
Dual water temperature regulator housing
(2) Water temperature regulator housing
(4) Bypass hose
(11) Water temperature regulator

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 (2) at the front right side of the cylinder head.

Water temperature regulator (11) 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 hose (4) and into the top inlet of the water pump. When the coolant temperature reaches the normal operating temperature, water temperature regulator (11) opens. When the water temperature regulator is open, the bypass is closed. Most of the coolant goes through bypass inlet (10) to the radiator for cooling. The remainder flows through bypass hose (4) and into the water pump.

Note: Coolant systems may contain one or two water temperature regulators.

The shunt line (9) extends from the top of the water pump to an expansion tank. The shunt line must be routed properly in order to avoid trapping any air. By providing a constant flow of coolant 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. The water temperature regulator divides coolant flow between the radiator 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.

Note: The air vent valve 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 in order to prevent coolant flow past the water temperature regulator.

For engines that have two water temperature regulators, the two regulators should have two different opening temperatures. The first regulator should operate as normal under light load conditions with the secondary regulator staying closed. As the engine is put under load, then the secondary regulator will open allowing the full flow of coolant to the radiator for cooling purposes.

Coolant For Air Compressor (If Equipped)



Illustration 6g01123298
(12) Coolant supply line
(13) Coolant return line

If the engine is equipped with an air compressor, coolant for the air compressor is supplied from the water temperature regulator housing, through coolant supply line (12). The coolant is circulated through the air compressor and the coolant is returned to the cooling system through coolant return line (13) 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 similar to the fuel filter and to 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 types of elements are the precharge element and the maintenance element. 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 in order for the coolant to flow through the elements after the conditioner material is 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 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.

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