Usage:
The engine is cooled by forced circulation of coolant by the water pump. The illustration below shows the coolant flow.
(1) Water Pump
Of a centrifugal type, the water pump is driven by the V-belt from the crankshaft pulley.
A unit seal is installed between the impeller and water pump that prevents leakage of coolant. There is a drain hole provided at the bottom of the water pump case, which ensures that coolant, should it leak from the unit seal, does not enter bearings.
<D3>
The water pump is mounted on the timing gear case provided with a suction pipe and swirl chamber.
Pressed into the one end of water pump shaft is the impeller with combination-type blades which feeds coolant under pressure into the engine.
<DR>
The water pump is installed at the front of crakcase.
An impeller with combination-type blades is press-fitted into one end of the water pump shaft.
(2) Thermostat
<D3>
The thermostat is bottom bypass type that stops supply of coolant to the bypass side when the path to the radiator becomes full open.
The thermostat pellet, of wax pellet type, contains a special wax which changes from a solid to liquid state and vice versa, depending on heat, and consequent change in its volume causes the valve to open or close, thereby changing the quantity of coolant which flows into the radiator and water pump (bypass side) to control the coolant temperature.
A jiggle valve is provided in the air purge hole of the thermostat to quickly increase the coolant temperature.
The jiggle valve is in down position by its own weight when the engine is stationary. When pouring in coolant, the air in the system is forced into the radiator through the clearance between the air purge hole and jiggle valve.
When the engine is started, coolant circulates and the jiggle valve is forced upward by the hydraulic pressure. As a result, the valve closes the air purge hole, preventing outflow of coolant through the air purge hole.
<DR>
The thermostat is a side bypass type which allows some cooling water to flow out to the bypass side even when the radiator side passage is in fully opened position.
The thermostat pellets are wax pellets same as D3.
(3) Radiator
The coolant is in many cases cooled by the radiator but the cooling capacity varies depending on applications (installation in an enclosed generator room of a building, operation in stationary state, etc.).
Considerations are, therefore, paid to the fan diameter, radiator capacity and other factors. Some units for construction plants are equipped with a oil cooler to cool hydraulic oil.
The pressure cap regulates the pressure in the cooling system. When the pressure builds up exceeding the predetermined level, the pressure valve compresses the pressure spring relieving the excessive pressure to the atmosphere.
As the coolant temperature falls forming a vacuum in the radiator, the vent valve opens to admit air into the radiator, thus preventing the radiator from being deformed by the vacuum.
When the pressure release lever is raised, the pressure valve opens, so the pressure in the cooling system can be reduced.
(4) Auto Cool Fan Coupling <Option: D3>
The auto cool fan coupling controls the fan speed according to the engine coolant temperature.
Control of the fan speed is accomplished by the bimetal which senses the temperature of air passing through the radiator to vary the quantity of hydraulic fluid of the fluid coupling.
When the temperature of air passing through the radiator is high, the bimetal at front end deforms, opening the valve in the storage chamber and circulates the hydraulic fluid (silicon oil) to increase the viscosity between the coupling case and rotor and the fan mounted to the case reaches a speed close to shaft speed. The viscosity (friction force) varies with the quantity of hydraulic fluid.
With a low air temperature, the valve closes by bimetal action and the hydraulic fluid is returned into the storage chamber by the pumping action of the operating chamber head. This generates slipping between the coupling case, and rotor, thus reducing the fan speed drastically.