NUT-FULL 1D4718 - Caterpillar

This engine has a pressure type cooling system that is equipped with a shunt line.A pressure type cooling system gives two advantages. First, the cooling system can be operated safely at a temperature that is higher than the boiling point of water. Also, cavitation in the water pump is prevented. It is more difficult for air or steam pockets to be made in the cooling system.Note: A 30 percent mixture of ethylene glycol base antifreeze must be used for efficient water pump performance on engines that are equipped with an air-to-air aftercooler. This mixture keeps the cavitation temperature range of the coolant high enough for efficient performance. Refer to Operation and Maintenance Manual, "General Coolant Information".
Illustration 1 g01096647
Cooling system for a warm engine (1) Cylinder head (2) Water temperature regulators (3) Outlet hose (4) Vent line (5) Vent tube (6) Shunt line (7) Elbow (8) Water pump (9) Cylinder block (10) Oil cooler (11) Inlet hose (12) RadiatorDuring operation, water pump (8) sends most of the coolant from radiator (12) to oil cooler (10) .The coolant from oil cooler (10) goes into cylinder block (9) through a bonnet and an elbow. The coolant flows around the cylinder liners into the cylinder head.The flow of coolant goes around the valves and the passages for exhaust gases in the cylinder head. The coolant then goes to the front of the cylinder head. At this point, two water temperature regulators (2) control the direction of coolant flow.Water temperature regulators (2) are closed when the engine is cold. The coolant flows through the regulator housing and elbow (7) back to water pump (8) .If the coolant is at normal operating temperature, water temperature regulators (2) open and the coolant flows to radiator (12) through the outlet hose (3). The coolant becomes cooler as the coolant moves through the radiator. When the coolant gets to the bottom of the radiator, the coolant goes through inlet hose (11) and into water pump (8) .Note: Water temperature regulators (2) are an important part of the cooling system. Water temperature regulator (2) divides the coolant flow between radiator (12) and bypass elbow (7). This will maintain the correct temperature.Shunt line (6) gives several advantages to the cooling system. The shunt line gives a positive coolant pressure at the water pump inlet that prevents pump cavitation. A small flow of coolant constantly goes through shunt line (6) to the inlet of water pump (8). This causes a small amount of coolant to move constantly through vent tube (5). The flow through the vent tube is small and the volume of the upper compartment is large. Air in the coolant is removed as the coolant goes into the upper compartment.The vent line is used to fill the cooling system with coolant for the first time. This will purge any air out of the top of a bottom filled system.A surge tank may be installed into the system. The tank can