Kubota D1803-CR-E4, Workshop Manual

Page: 161 / 309

7.2 Feature of cooling system
The cooling system prevents overheating while the
engine is running and maintains coolant temperature at
a suitable temperature during operation.
KUBOTA engines use a cooling system with forced
circulation using a water pump.
This series of engines use a bottom bypass system.
The bottom bypass system improves the cooling
performance of the radiator.
7.3 Flow of cooling system (Bottom
by-pass system)
(1) Thermostat
(A) When thermostat closes (B) When thermostat opens
(2) Cylinder head
(3) By-pass
(4) Water pump
(5) Crankcase
(6) Cylinder head (7) Radiator
(8) Water pump
(9) Crankcase
(A) When thermostat closes
(B) When thermostat opens
(A) When thermostat closes
1. The bypass is open while coolant temperature in
the engine is low.
2. Here, coolant circulates in the engine through the
bypass.
(B) When thermostat opens
1. When coolant temperature reaches the thermostat
valve open temperature, the valve closes the
bypass.
2. As the bypass is closed, warmed coolant flows to
the radiator and is cooled.
3. Coolant that has been cooled in the radiator is
returned to the engine by the water pump.
7.4 Control of cooling system
(Bottom by-pass system)
The cooling system includes a coolant temperature
sensor that fulfills the following roles.
1. Suppressing overheating of engine.
2. Conditions during difference learning of the supply
pump device (coolant temperature 65
℃
(149
℉
)or
higher).
3. Conditions for regeneration of the DPF (coolant
temperature 50
℃
(122
℉
) or higher).
7.5 Water pump
7.5.1 Outline of water pump
The water pump force circulates coolant inside the
system.
7.5.2 Structure of water pump
The water pump is made up of a mechanical seal and
impeller and the like.
The water pump is mounted on the same shaft as the
cooling fan and fan pulley.
MECHANISM
7. Cooling system 4. ENGINE
D1803-CR-E4,D1803-CR-TE4,D1803-CR-TIE4,V2403-CR-E4,V2403-CR-TE4,V2403-CR-TE4BG,V2403-CR-TIE4
4-61
KiSC issued 12, 2018 A