19-3
3. INDEPENDENT CYLINDER HEAD/CYLINDER BLOCK COOLING SYSTEM
STRUCTURE AND FEATURES
The cylinder head and cylinder block cooling passages are laid out independently from each other, each of which is
equipped with the thermostat to control the cooling water temperature of each passage.
Structure:
• The cooling water supplied from the water pump with force flows through the water tube and oil case, then it is drawn
into the mounting case.
In the mounting case, the cooling water separates into the two independent flows; one that goes to the cylinder head
and the other that goes to the cylinder block.
The cooling water temperature of each flow is regulated by the thermostat located at the outlet port of each passage.
• The thermostat valve open temperature for the cylinder head cooling water and for the cylinder block cooling water are
set at different temperature from each other.
At the cylinder block side, the thermostat valve open temperature is set at the optimum temperature (60˚C) to prevent
oil dilution (over-cooling) during cruising at low speeds with extremely low load.
At the cylinder head side, the thermostat valve open temperature is set at the temperature (50˚C) that can enhance the
knocking limit by flushing the water more. Setting the valve open temperature in this way realized improvement in
engine horsepower as well as toughness of the cylinder head against overheating.
COOLING CIRCUIT DIAGRAM
THERMOSTAT A (50˚C)
(FOR HEAD)
THERMOSTAT B (60˚C)
(FOR BLOCK)
OIL FILTER
FLANGE
RELIEF VALVE
WATER TUBE
BLOCK COOLING
PASSAGES
VAPOR
SEPARATOR
HEAD COOLING
PASSAGE
BRANCHING
CHAMBER
WATER
CHECK HOLE
INLET WATER
RETURN
WATER
WATER
PUMP