TM 9-6115-729-24
0003
ENGINE COOLING SYSTEM
The engine cooling system (Figure 5) consists of a radiator, hoses, thermostat, water pump, surge tank and
expansion bottle, a belt driven fan, and cooling jackets. The water pump forces coolant through passages
(cooling jackets) in the engine block and cylinder head where the coolant absorbs heat from the engine. When
the engine reaches normal operating temperature, the thermostat opens and the heated coolant flows through
the upper radiator hose assembly into the radiator. The cooling fan circulates air through the radiator where the
coolant temperature is reduced. In addition, the fan cools engine and generator set components within the TQG
housing by drawing in air from outside the housing through the baffles, circulating the air through the housing and
forcing the air through the radiator and out through the housing exhaust vents on the roof. The housing is
designed to operate with the doors closed which ensures that the main alternator and other TQG components
have access to a good flow of cooling air from outside the generator set. The normal operating temperature of
the generator set is 170 F to 200 F (77 C to 93 C). A coolant temperature sensor provides automatic shut
down in the event that coolant temperature exceeds 230F (110C). The TQG engine has a pressurized cooling
system equipped with a shunt line. The cooling system can operate safely at temperatures higher than the
normal boiling point of water without water pump cavitation. 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 prevents water pump cavitation by providing a constant flow of
coolant. The water pump is located on the right side of the cylinder block. The water pump is belt driven from the
crankshaft pulley. Coolant can enter the water pump from via the inlet at the bottom of the water pump, through
the bypass hose into the top of the water pump, and through the shunt line 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 in the engine block.
