User's Manual

COOLING SYSTEM 4-5
Coolant Flow Chart
1. Drain Bolt
2. Water Pump
3. Cylinder Jacket
4. Cylinder Head Jacket
5. Thermostat Housing
6. Radiator Cap
7. Radiator
8. Oil Filter
9. Reserve Tank
10. Reserve Tank Hose
11. R eserve Tank Overflow Hose
12. Radiator Fan
13. Water Temperature Sensor
14. Radiator Fan Switch
15. Hot Coolant
16. Cold Coolant
17. Front
Permanent type antifreeze is used as a coolant to protect the cooling system from rust and corro-
sion. When the engine starts, the water pump turns and the coolant circulates.
The thermostat is a wax pellet type which opens or closes with coolant temperature changes. The
thermostat continuously changes its valve opening to keep the coolant temperature at the proper level.
When coolant temperature is 55°C (131°F) or more, the thermostat closes so that the c oolant flow is
restricted through the air bleeder hole, causing the engine to warm up more quickly. When coolant
temperature is more than 58 ∼ 62°C (136 ∼ 144°F), the thermostat opens and the coolant flows.
When the coolant temperature goes up beyond 95 ∼ 101°C (203 ∼ 214°F), the radiator fan switch
conducts to operate t he radiator fan. The radiator fan draws air through the radiator core when there
is not sufficient air flow such as at low speeds. This increases up the cooling action of the radiator.
When the c oolant temperature goes down from the operation temperature by 3 ∼ 8°C (37 ∼ 46°F), the
fan switch opens and the radiator fan stops.
In this way, this system controls the engine temperature within narrow limits where the engine op-
erates most efficiently even if the engine load varies.
The system is pressurized by the radiator cap to suppress boiling and the resultant air bubbles
which can cause engine overheating. As the engine warms up, the coolant in the radiator and the
water jacket expands. The excess coolant flows t hrough the radiator cap and hose to the reserve tank
to be stored there t emporarily. Conversely, as the engine cools down, the coolant in the radiator and
the water jacket contracts, and the stored coolant flows back to the radiator from the reserve tank.
The radiator cap has two valves. One is a pressure valve w hich holds the pressure in the system
when the engine is running. When the pressure exceeds 93 ∼ 123 kPa ( 0.95 ∼ 1.25 kgf/cm², 14 ∼ 17.8
psi), the pressure valve opens and releases the pressure to the reserve tank. As soon as pressure
escapes, the valve closes, and keeps the pressure at 93 ∼ 123 kPa (0.95 ∼ 1.25 kgf/cm², 14 ∼ 17.8
psi). When the engine cools down, another small valve (vacuum valve) in the cap opens. As the
coolant cools, the coolant contracts to form a vacuum in the system. The vacuum valve opens and
allows the coolant from the reserve tank to enter the radiator.