Description

This engine utilizes a pressurized forced circulation cooling system which includes a thermostat equipped with a by-pass valve mounted on the inlet side.

3S-GTE

Throttle Body

ISC Valve

Water By-Pass Pipe (No. 1 Air Tube)

Water Pump

Throttle Body

ISC Valve

Water By-Pass Pipe (No. 1 Air Tube)

Water Pump

Toyota Corolla Water Jacket Plug

Water Outlet TO HEATER

TO RADIATOR

"Turbo Water Pipe

Thermostat

FROM RADIATOR

Turbocharger

Water Inlet

Water Outlet TO HEATER

TO RADIATOR

"Turbo Water Pipe

Thermostat

FROM RADIATOR

Turbocharger

Water Inlet

5S-FE

ISC Valve

Throttle Body

Water Pump-

ISC Valve

Throttle Body

Toyota Mr2 Fuel Gauge Gas Tank

Water Outlet

\ TO RADIATOR

Thermostat

Water By-Pass Pipe

Water Inlet

Water Outlet

\ TO RADIATOR

Thermostat

4 Oil Cooler FROM RADIATOR

4 Oil Cooler FROM RADIATOR

Water By-Pass Pipe

Water Inlet

C009801

C00981

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 an electric fan blows 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

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 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 left tank to the right tank as well as cooling fins which rediate heat away from the coolant in the tubes. Air sucked in by the electric cooing fan, as well as the wind generayed by the vehicle's travel, passes through the radiator, cooling the coolant heated by the water jecket as it passes through the tubes in the core. Models with automatic transmission include an automatic transmission fluid cooler incorpo rated into the cooling pipes. 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

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 coolant from boiling even when the coolant temperature exceeds 100°C (212°F). A relief valve (pressurization valve) and a vacuum valve (negative >ressure 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: 110-120°C, 230 - 248°F, pressure; 0.3 - 1.0 kg/cm2, 4.3 -14.2 psi, 29.4 - 98.1 kPa). 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.

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 radiator 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 by-pass valve and is mounted in the water inlet housing. The thermostat includes a type of automatic valve operated by fluctuations in the coolant temperature. 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 xhe valve closed, thus opening the valve. When the wax cools, its contraction causes the force of the spring take effect once more, closing the valve. The thermostat in this engine operates at a temperature of 82°C (180°F).

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