4TNV98 & 4TNE98 Diesel Engine Section 1. General Service Information11Function of Cooling System ComponentsComponents FunctionsCooling SystemThe TNV engine is liquid-cooled by means of a cooling system. Thecooling system consists of a radiator, radiator cap, engine coolingfan, engine coolant pump,thermostat, and reserve tank. Note thatall cooling system components are required for proper engineoperation. Since some of the components are applicationspecific, they must be carefully selected by an applicationengineer. The application specific items are not part of thebasic 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 thecrankshaft V-pulley. The purpose of the engine cooling fan is tocirculate air through the radiator.Engine Coolant Pump The engine coolant pump circulates the engine coolant through thecylinder block and the cylinder head and returns the engine coolantto the radiator.RadiatorThe radiator acts as a heat exchanger. As the engine coolantcirculates through the cylinder block it absorbs heat. The heat in theengine coolant is dissipated in the radiator. As the engine cooling fancirculates air through the radiator, the heat is transferred to the air.Radiator CapThe radiator cap controls the cooling system pressure. The coolingsystem is pressurized to raise the boiling point of the engine coolant.As the engine coolant temperature rises, the system pressure andthe coolant volume increases. When the pressure reaches a presetvalue, the release valve in the radiator cap opens and the excessengine coolant flows into the reserve tank. As the engine coolanttemperature is reduced, the system pressure and volume is reducedand the vacuum valve in the radiator cap opens allowing the enginecoolant to flow from the reserve tank back into the radiator.Reserve TankThe reserve tank contains the overflow of engine coolant from theradiator. If you need to add engine coolant to the system, add it tothe reserve tank; not the radiator.ThermostatA thermostat is placed in the cooling system to prevent the enginecoolant from circulating into the radiator until the engine coolanttemperature reaches a preset temperature. When the engine is cold,no engine coolant flows through the radiator. Once the enginereaches its operating temperature, the thermostat opens and allowsthe engine coolant to flow through the radiator. By letting the enginewarm up as quickly as possible, the thermostat reduces enginewear, deposits and emissions.
