GENERAL SERVICE INFORMATION
TNV DI Service Manual
4-11
Function of Cooling System Components
FUNCTION OF COOLING SYSTEM COMPONENTS
Components
Functions
Cooling System
The TNV engine is liquid-cooled by means of a cooling system. The cooling system
consists of a radiator, radiator cap, engine cooling fan, engine coolant pump,
thermostat, and reserve tank. Note that all cooling system components are
required for proper engine operation. Since some of the components are
application specific, they must be carefully selected by an application
engineer. The application specific items are not part of the basic engine
package as shipped from the Yanmar factory.
Engine Cooling Fan
The engine cooling fan is driven by a V-belt which is powered by the crankshaft
V-pulley. The purpose of the engine cooling fan is to circulate air through the
radiator.
Engine Coolant Pump
The engine coolant pump circulates the engine coolant through the cylinder block
and the cylinder head and returns the engine coolant to the radiator.
Radiator
The radiator acts as a heat exchanger. As the engine coolant circulates through
the cylinder block it absorbs heat. The heat in the engine coolant is dissipated in
the radiator. As the engine cooling fan circulates air through the radiator, the heat
is transferred to the air.
Radiator Cap
The radiator cap controls the cooling system pressure. The cooling system is
pressurized to raise the boiling point of the engine coolant. As the engine coolant
temperature rises, the system pressure and the coolant volume increases. When
the pressure reaches a preset value, the release valve in the radiator cap opens
and the excess engine coolant flows into the reserve tank. As the engine coolant
temperature is reduced, the system pressure and volume is reduced and the
vacuum valve in the radiator cap opens allowing the engine coolant to flow from
the reserve tank back into the radiator.
Reserve Tank
The reserve tank contains the overflow of engine coolant from the radiator. If you
need to add engine coolant to the system, add it to the reserve tank; not the
radiator.
Thermostat
A thermostat is placed in the cooling system to prevent the engine coolant from
circulating into the radiator until the engine coolant temperature reaches a preset
temperature. When the engine is cold, no engine coolant flows through the
radiator. Once the engine reaches its operating temperature, the thermostat opens
and allows the engine coolant to flow through the radiator. By letting the engine
warm up as quickly as possible, the thermostat reduces engine wear, deposits and
emissions.
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