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 TM 55-1925-273-10-1
OPERATOR'S MANUAL
INLAND AND COASTAL LARGE TUG (LT)
THEORY OF OPERATION
ENGINE COOLING SYSTEMS
GENERAL
Several different types of engine cooling systems are used on board the LT. Both main engines, and both Ship's Service
Diesel Generator (SSDG) engines utilize keel cooler systems (figure 1). The Emergency Diesel Generator (EDG) uses a
radiator cooling system (figure 2). The bow thruster and pump drive engines use heat exchanger systems (figure 3). The
paragraphs below describe each of these cooling systems in detail.
ENGINE COOLING SYSTEM COMPONENTS
ENGINE COOLANT
All engines described use engine coolant. The engine coolant is a mixture of water and ethylene glycol antifreeze. This
mixture of water and antifreeze protects against freezing, overheating, and corrosion. A 50/50 mixture of ethylene glycol
antifreeze and water will freeze at 34 F (-36.7 C), which is significantly lower than the freezing temperature of water
alone. The same 50/50 mixture has a boiling point of up to 276F (135.6 C) depending upon cooling system pressure.
Ethylene glycol antifreeze also contains additives that help prevent corrosion of system components.
CENTRIFUGAL PUMPS
Centrifugal pumps circulate the engine coolant throughout the cooling system on each engine.
COOLANT PASSAGES
Coolant passages route engine coolant to and around cylinders, cylinder heads, and other vital components.
OIL COOLER
Oil coolers provide cooling for oil that is heated while lubricating the engine.
AFTERCOOLER
Engine coolant is circulated through the aftercooler, which is located in the turbocharger air discharge duct, to cool the
intake air before it enters the engine.
EXPANSION TANK
The expansion tank (figure 1, item 1) is a reservoir for the coolant. It is the highest place in the cooling system. The volume
of the coolant can change in the expansion tank without affecting the coolant level in the remainder of the cooling system.
PRESSURE CAP
The expansion tank (figure 1, item 1) in conjunction with the pressure cap (figure 1, item 2) controls the pressure of the
cooling system. Excessive coolant pressure will vent through the pressure cap.
RAW WATER STRAINER
A raw water strainer filters out large debris that may block or contaminate the cooling systems.
SEACHEST
The seachest is a compartment (three in quantity) located near the center line on the bottom of the vessel. This is where raw
water is drawn into the vessel cooling systems to provide firefighting water, and to make fresh water.
0018 00-1
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