Toyota 3S-GE Repair Manual page 313

_ ENGINE — COOLING SYSTEM
EG-299
RADIATOR RESERVOIR
The reservoir is used to catch coolant which overflows the cooling system as a result of
volumetric expansion when the coolant is heated. The coolant in the reservoir returns to the
radiator when the coolant temperature drops, thus keeping the radiator full at all times and
avoiding needless coolant loss.
Check the reservoir level to learn if the coolant needs to be replenished.
WATER PUMP
The water pump is used for forced circulation of coolant through the cooling system. It is
mounted on the front of the cylinder block and driven by a timing belt.
THERMOSTAT
The thermostat has a wax type bypass valve and is mounted in the water inlet housing. The
thermostat includes a type of automatic valve operated by fluctuations in the coolant tempera-
ture. This valve closes when the coolant temperature drops, preventing the circulation of coolant
through the engine and thus permitting the engine to warm up rapidly. The valve opens when the
coolant temperature has risen, allowing the circulation of coolant. Wax inside the thermostat
expands when heated and contracts when cooled. Heating the wax thus generates pressure
which overpowers the force of the spring which keeps the valve closed, thus opening the valve.
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).