Cooling System; Thermostat - Kubota KX080-3 Workshop Manual

WSM KX080-3 Service

4. COOLING SYSTEM

[1] THERMOSTAT

Conventional
(outlet water temperature control type) open against the
flow of coolant. In this design, the pressure (steam
pressure + water pump's discharge pressure) affects the
open/close performance of such valve. In other words,
the valve may be delayed in opening at a preset opening
temperature opening suddenly, above the preset
temperature. This is called the overshoot phenomenon.
The overshoot problem invites the undershoot
phenomenon too.
radiator flows through the water passage, which
suddenly closes the valve below the thermostat's preset
valve closing temperature.
A repeated cycle of such overshoot and undershoot
phenomena is called the water temperature hunting.
This hunting problem may adversely affects the cooling
system parts, and also the engine and its related
components.
To cope with this trouble, the V3 series engine is
equipped with the flow control thermostat. The valve
has a notch to control the coolant flowrate smoothly in
small steps.
(1) Coolant Temperature
(2) Time
(3) Overshoot
(4) Notch
III-S-78
thermostatically-controlled
Too much water cooled by the
(A) Valve Lift Versus Flowrate
(B) Flowrate
(C) At Short Valve Lift
(D) At Medium Valve Lift
(E) At High Valve Lift
(F) Valve Lift
Engine
valves
W1013684