Service Manual

4-4 COOLING SYSTEM
Coolant Flow Chart
Permanent type antifreeze is used as a coolant to protect the cooling system from rust and corrosion.
When the engine starts, the water pum p turns and the coolant circulates.
The thermostat is a wax pellet type which opens or closes as coolant temperature changes. The
thermostat continuously changes its valve opening to keep the coolant temperature at the proper level.
When coolant temperature is below 58 ∼ 62°C (136 ∼ 144°F), the thermostat closes so that the coolant
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 100 ∼ 110°C (212 ∼ 230°F), the radiator fan switch
conducts 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 low speeds. This increases up the cooling action of the radiator.
When the temperature is below 97 ∼ 103°C (207 ∼ 217°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 r adiator and the
water jacket expands. The excess coolant flows through the r adiator cap and hose to t he reserve tank
to be stored there temporarily. Conversely, as t he 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 r eserve 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 from a vacuum in the system. The vacuum valve opens
and allows the coolant from the reserve tank to enter the radiator.