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 TM 55-1905-242-14
0003 00
ENGINE COOLING SYSTEM
The propulsion engines are cooled by a mixture of water and ethylene glycol antifreeze. This mixture of water and anti-
freeze 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 276 F (135.6 C), depending upon cooling system pressure. Ethylene glycol antifreeze also
contains additives that help prevent corrosion of cooling system components.
EXPANSION TANK
GAUGE
GLASS
SWING CHECK
VALVE
KEEL COOLER
ENGINE COOLING SYSTEM
The engine coolant is circulated through the closed loop cooling system by an engine-driven centrifugal water pump. As the
coolant circulates through the engine, it absorbs heat from the engine's cylinder block, cylinder heads, exhaust manifold
surfaces, and from the engine oil and the marine transmission oil. After circulating through the engine, the coolant passes
through a keel cooler that is longitudinally recessed in the hull between frames 25 and 31. As the coolant circulates through
the keel cooler, the heat absorbed from the engine is transferred to the raw water outside the hull. After the coolant has
passed through the keel cooler, it reenters the engine through a swing check valve to begin the cooling cycle again.
Engine coolant temperature is regulated by thermostats mounted in the propulsion engines. These thermostats regulate
coolant temperature by controlling the flow of coolant through the system. When the coolant is cold, it is recirculated
through the engine cooling passages without passing through the keel cooler. When the coolant reaches operating tempera-
ture, a portion of the coolant is circulated through the keel cooler for cooling. Flow through the keel cooler will vary
depending upon many variables, including coolant temperature, raw water temperature, and engine load conditions.
The engine cooling system has an expansion tank mounted on the engine room bulkhead directly forward of the engine. The
expansion tank allows coolant expansion and contraction and allows access to the system for filling and/or resupplying the
system.
0003 00-2
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