C3.3B Tier 4 Interim and EU Stage 3A Engines for Caterpillar Built Machines – Cooling System




Illustration 1g03002312

(1) Radiator

(2) Water Pump

(3) Cooling Fan

(4) Water Temperature Regulator

(5) Cylinder Head

(6) Cylinder Block

This engine utilizes a pressure type cooling system.

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 reduced. A pressurized cooling system also helps to prevent air or steam pockets forming in the cooling system.

Bottom Bypass System

These engines have a bottom bypass system to enhance the cooling performance.

While the temperature of coolant in the engine is low, thermostat (4) remains is in the closed position. Coolant is allowed to flow through the bypass pipe, and is circulated through the engine block. When coolant temperature exceeds the thermostat valve opening level, the thermostat opens in order to prevent coolant from flowing through the bypass pipe into the engine.



Illustration 2g03002339

View of bypass valve opened

(4) Water Temperature Regulator




Illustration 3g03002342

View of bypass valve closed

(4) Water Temperature Regulator

When the temperature of the coolant in the engine is low, the water temperature regulator stays closed. When the regulator is closed, the coolant flows through the bypass pipe and around the engine.

When the temperature is more than the water temperature regulator valve opening level, the water temperature regulator opens up fully. The hot coolant cannot flow through the bypass into the engine and can flow into the radiator. The radiator can decrease the temperature of the coolant more easily.

Water Pump




Illustration 4g03001862

(7) Water pump

(8) Gasket

The water pump circulates the coolant through the system.

If the pump fails to circulate the coolant, heat is not removed from the engine and overheating damage may occur.

These engines use a centrifugal type water pump, and the pump driven by the crankshaft by a fan belt. The water pump is composed of a pump body, impeller, mechanical seal, and bearing assembly.

Cooling Fan




Illustration 5g02797182

(A) Suction Type Cooling Fan

(B) Blower Type Cooling Fan

The cooling fan is located on the water pump shaft with a fan pulley, and is driven by a V-belt from the engine crankshaft.

The cooling fan is comprised of a steel or synthetic resin. Fans blower capacity varies according to the number of blades, twisting angle, outside diameter and rotating speed.

Generally, large diameter cooling fan provides sufficient cooling air at low rotating speed. However, the same cooling effect can be obtained with a smaller diameter fan by providing higher fan speed or fan blades with a steep-blade angle. This allows a more compact installation.

The fan can be either a suction type or a blower type, depending upon the design of the system.

Suction type cooling fan. This fan pulls air through the radiator and pushes air over the engine. This design permits the use of a smaller fan and radiator than is required for blower type fan. This type of fan is utilized when machine motion aids air movement through the radiator.

Blower type cooling fan. This fan pulls air across the engine, then pushes air through the radiator. This type is used in slow-moving machine, and on machine where harmful materials might be drawn into the radiator with a suction type fan.

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