Function Of Water Pump; Thermostat; Outline Of Thermostat; Structure Of Thermostat - Kubota D1803-CR-E4 Workshop Manual

4. ENGINE
(1) Bearing unit
(2) Pump body

7.5.3 Function of water pump

The water pump is driven by the crankshaft via the fan
belt, fan pulley, and fan drive pulley.
Coolant is suctioned into the impeller rotating at high
speed, pressurized by the centrifugal force, and fed to
the crankcase water jacket.
The mechanical seal provided between the bearing and
pump chamber prevents leaking of the coolant.

7.6 Thermostat

7.6.1 Outline of thermostat

The thermostat opens and closes the coolant path
based on the engine coolant temperature.
The thermostat maintains coolant at a suitable
temperature.

7.6.2 Structure of thermostat

The thermostat is made up of a pellet, bypass valve,
and spring and the like.
(1) Valve
(2) Spring
(3) Pellet
4-62
(3) Mechanical seal
(4) Impeller
(4) Bypass valve
(5) Jiggle valve
D1803-CR-E4,D1803-CR-TE4,D1803-CR-TIE4,V2403-CR-E4,V2403-CR-TE4,V2403-CR-TE4BG,V2403-CR-TIE4

7.6.3 Function of thermostat

(A) When coolant temperature is
low (valve is closed)
The thermostat opens and closes the coolant path
based on the engine coolant temperature to maintain
suitable temperature.
(A) When coolant temperature is low (valve is
closed)
The wax inside the pellet is solidified so that the valve
of the thermostat is closed by the spring.
Also, the bypass part is opened by the bypass valve.
(B) When coolant temperature is high (valve is
open)
The wax inside the pellet liquefies and expands
pushing down the valve and opening the thermostat.
Here, the bypass valve closes the bypass part.
The jiggle valve is a valve to prevent build up of air
inside the thermostat.
(A) Coolant temperature
(B) Time (min)

7.6.4 Specification of thermostat

Coolant suitable temperature
MECHANISM
7. Cooling system
(B) When coolant temperature is
high (valve is open)
(C) Overshoot
85 to 95 ℃
185 to 203 ℉
KiSC issued 12, 2018 A