1.17. ENGINE COOLING SYSTEM

TM 5-3895-373-20 1.17. ENGINE COOLING SYSTEM. The engine cooling system is a closed loop system; engine coolant is contained and recirculated within the system. The system includes a radiator, radiator fan, water pump, engine water jacket, and thermostat. A remote mounted engine oil cooler is also included. Engine coolant flow through the oil cooler removes excess heat from the engine oil as it recirculates through the oil filter manifold and oil filter. Ancillary devices (not shown) include a water temperature sensor and gauge, a high temperature shutdown sensor and fuel shutoff solenoid, and a DCA transducer. The radiator fan and water pump are belt driven by the engine crankshaft pulley. The water pump circulates coolant whenever the engine is running. The pump directs the coolant flow into a water jacket that surrounds the engine cylinders and cylinder head. The water jacket channels the output flow from the water pump to the bottom of the engine. A thermostat housing is located at the top of the engine. Increased fluid pressure within the water jacket forces coolant to flow through either a bypass port or output port in the thermostat housing. The bypass port leads to the input side of the water pump. The output port is connected to the radiator input port. A pair of coolant hoses also provides a continuous flow of coolant to and from the engine oil cooler. When the engine is first started, the thermostat is closed. The closed thermostat opens the bypass port to the water pump and shuts off coolant flow to the radiator. The coolant continues to recirculate through the water pump, oil cooler, and water jacket while the engine warms up. When the temperature of the recirculating coolant reaches 177°F (80°C), the thermostat starts to open, which diverts some of the coolant flow from the bypass port to the radiator input port. When the coolant temperature reaches 208°F (98°C), the thermostat completely opens. The fully open thermostat shuts off the bypass port, which sends the full flow of coolant to the radiator input port. Increased fluid pressure within the radiator forces an equal volume of coolant out of the radiator output port and back to the water pump. While the heated coolant flows through the radiator, the radiator fan pulls a flow of outside air through the radiator cooling fins, which removes heat from the recirculating coolant. At normal engine operating temperatures, the expected temperature drop across the radiator circuit (input port to output port) is approximately 10°F (5°C). 1-21