Reservoir Tank - Toyota 1 MZ–FE Manual

RADIATOR CAP (on water outlet)
The radiator cap is a pressure–type cap which seals the engine coolant circuit and the resulting
pressurization of the engine as the coolant expands. The pressurization prevents the coolant from
boiling even when the coolant temperature exceeds 1002C (2122F). 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 through the overflow pipe when the pressure generated inside the
cooling system exceeds the limit (coolant temperature: 110 – 1202C (230 – 2482F), pressure:
83 – 113 kPa (0.85 – 1.15 kgf/cm
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.

RESERVOIR TANK

The reservoir tank 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 tank returns to the
water outlet when the coolant temperature drops thus keeping the radiator full at all times and
avoiding needless coolant loss. Check the reservoir tank 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 822 C (1802 F).
ELECTRONICALLY CONTROLLED HYDRAULIC COOLING FAN (See page EG2–346)
1MZ–FE ENGINE –
2
,12.1 – 16.4 psi). The vacuum valve opens to alleviate the
COOLING SYSTEM
EG2–315