C7 Engines for Caterpillar Built Machines Cooling System Caterpillar


Cooling System
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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 1g01103269
(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 which is located on 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 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.

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.

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 hose (4) 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 bypass inlet to the radiator for cooling. The remainder flows through bypass hose (4) and into the water pump.

Note: Some coolant systems may contain 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: 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 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.

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