Toyota 3S-GE Repair Manual page 312

EG 298
ENGINE — COOLING SYSTEM
The cooling system is composed of the water jacket (inside the cylinder block and cylinder head),
radiator, water pump, thermostat, electric fan, hoses and other components.
Coolant which is heated in the water jacket is pumped to the radiator, through which the electric
fan draws air to cool the coolant as it passes through. Coolant which has been cooled is then sent
back to the engine by the water pump, where it cools the engine.
The water jacket is a network of channels in the shell of the cylinder block and cylinder head
through which coolant passes. It is designed to provide adequate cooling of the cylinders and
combustion chambers which become heated during engine operation.
RADIATOR (ST202)
The radiator performs the function of cooling the coolant which has passed through the water
jacket and become hot, and it is mounted in the front of the vehicle. The radiator consists of an
upper tank and lower tank, and a core which connects the 2 tanks. The upper tank contains the
inlet for coolant from the water jacket and the filler inlet. It also has a hose attached through
which excess coolant or steam can flow. The lower tank has an outlet and drain cock for the
coolant. The core contains many tubes through which coolant flows from the upper tank to the
lower tank as well as to cooling fins which radiate heat away from the coolant in the tubes. The
air drawn through the radiator by the electric fan, as well as the wind generated by the vehicle's
motion, passes through the radiator, cooling the coolant. A fan with an electric motor is mounted
behind the radiator to assist the flow of air through the radiator. The fan operates when the
engine coolant temperature becomes high in order to prevent it from becoming too high.
RADIATOR (SW20)
The radiator cools the coolant which has passed through the water jacket and become hot, and
it is mounted in the front of the vehicle. The MR2 radiator is different from that in other models,
in that it is a cross flow type in which the coolant flows horizontally. It includes side tanks and a
core which connects them. The inlet for coolant from the water jacket and the drain cock for
draining out coolant are located in the left tank. The outlet coolant and an air drain, which
facilitates the supply of coolant to the engine are located in the right tank. The core contains
many tubes through which coolant flows from the left tank to the right tank as well as cooling fins
which radiate heat away from the coolant in the tubes. Air drawn in by the electric cooling fan,
as well as the wind generated by the vehicle's motion, passes through the radiator, cooling the
coolant heated in the water jacket as it passes through the tubes in the core. A fan with an
electric motor is mounted behind the radiator to assist the flow of air through the radiator. The
fan operates when the coolant temperature becomes high in order to prevent it from becoming
too high.
RADIATOR CAP (ST202). WATER FILLER CAP (SW20)
The radiator (water filler) cap is a pressure type cap which seals the radiator resulting in
pressurization of the radiator as the coolant expands. The pressurization prevents the coolant
from boiling even when the coolant temperature exceeds 100°C (212° F). A relief valve (pre-
ssurization valve) and a vacuum valve (negative pressure valve) are built into the radiator (water
filler) cap. The relief valve opens and lets steam escape through the overflow pipe when the
pressure generated inside the cooling system exceeds the limit (coolant temperature: 110 —
120°C (230 — 248°F), pressure; 59 — 103 kPa (0.60 — 1.05 kgf/cm', 8.5 — 14.9 psi). The
vacuum valve opens to alleviate the vacuum which develops in the coolant system after the
engine is stopped and the coolant temperature drops. The valve's opening allows the coolant in
the reservoir tank to return to the cooling system.