lower tank. Air passing over the radiator fins cools the heated engine coolant flowing through the
radiator.
The upper tank has an inlet for engine coolant from the water jacket and it has a filler inlet. It also
has a hose attached through which excess engine coolant or steam can flow. The lower tank has
an outlet for the engine coolant and a drain cock. Automatic transmission models include an
automatic transmission fluid cooler.
RADIATOR CAP
The radiator cap is a pressure type cap which seals the radiator, resulting in pressurization of the
radiator as the coolant expands. The pressurization prevents the engine coolant from boiling even
when the engine coolant temperature exceeds 100* C (212. F).
A relief valve (pressurization valve) and a vacuum valve (negative pressure valve) are built into the
radiator cap. The relief valve opens and lets steam escape out of the overflow pipe when the
pressure generated in the cooling system exceeds the limit (engine coolant temperature: 110 –
120 C 230 – 248 ”F, pressure: 58.8 – 103.0 kPa, 0.6 – 1.05 kgf/cm2, 8.5 – 14.9 psi). The
vacuum valve opens to allow engine coolant to enter in order to alleviate the vacuum which
develops in the engine coolant system after the engine has stopped and the engine coolant
temperature drops.
RESERVOIR TANK
The reservoir tank is used to catch engine coolant which–overflows the cooling system as a result
of volumetric expansion when the engine coolant is heated. When the engine coolant temper–
ature drops, engine coolant in the reservoir tank returns to the radiator, thus keeping the radiator
full at all times and avoiding needless engine coolant loss. To find out if the engine coolant needs
to be replenished, check the reservoir tank level.
WATER PUMP
The water pump is used for forced circulation of engine coolant through the cooling system. It is
mounted on the front of the engine block and driven by the timing belt.
THERMOSTAT
The thermostat has a wax type by–pass valve and is mounted in the water inlet housing. The
thermostat includes a type of automatic valve operated by fluctuations in the engine coolant
temperature. When the engine coolant temperature is low, the valve closes to prevent the engine
coolant flowing to the radiator, thus permitting the engine to warm up rapidly. When the by–
pass valve opens the by–pass circuit, the engine coolant continues to circulate inside the engine,
quickly and uniformly warming up to the operating temperature.
When the engine coolant temperature is high, the valve opens and the engine coolant flows to the
radiator where it is cooled. When the wax inside the thermostat is heated, it expands and thus
creates pressure which overpowers the force of the spring which keeps the valve closed. When
the wax cools, its contraction allows the force of the spring to take effect once more, closing the
valve. The thermostat in this engine operates at a temperature of 82 C (180 F).
–ENGINE COOLING SYSTEM
EG2–262
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