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COOLING SYSTEM 4-5
Coolant Flow Chart
1. Drain Bolt
2. Water Pump
3. Cylinder Jacket
4. Cylinder Head Jacket
5. Thermostat Housing
6. Thermostat Air Bleeder
Bolt
7. Radiator Cap
8. Radiator
9. Oil Filter
10. Outlet Hose
11. Inlet Hose
12. Oil Cooler
13. Reserve Tank
14. Reserve Tank Hose
15. Reserve Tank Overflow
Hose
16. Radiator Fan
17. Water Temperature Sen-
sor
18. Radiator Fan Switch
19. Hot Coolant
20. Cold Coolant
21. Front
Permanent type antifreeze is used as a coolant to protect the cooling system from rust and corrosion.
When the engine starts, the w ater pump turns and the coolant circulates.
Th
e 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 less than 55 ° (131 °F), the thermostat closes so that the coolant flow
i
s 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 93 ∼ 103 °C (199 ∼ 217 °F), the radiator fan switch
c
onducts to operate the radiator fan. The radiator fan draws air t hrough the radiator core when there
is not sufficient air flow such as at l ow speeds. This increases up the cooling action of the radiator.
When the temperature is below 85 ∼ 100 °C (185 ∼ 212 °F), the fan switch opens and the radiator fan
s
tops.
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.
T
he 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 temporarily. 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 which holds the pressure in the system
when the engine is running. When the pressure exceeds 93 ∼ 123 kPa (0.95 ∼ 1.25 kgf/cm², 13.5
∼ 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,
13.5 ∼ 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.