General Engine Cooling System Information

The closed-type cooling system consists of a water pump, a cross-flow radiator, a coolant reserve tank, an electric cooling fan, a thermostat, a heater core, hoses and sensors. On 4A-FE engines, the water pump is driven by the timing belt from the crankshaft pulley; the water pump pulley also drives the power steering pump (if equipped). On 3S-FE engines, the water pump is driven by the camshaft drive belt.

The system operates as follows. The water pump circulates cold coolant through the cylinder block, cylinder head passages, throttle body and heater core.

While the engine is cold, coolant returns from the thermostat housing to the water pump. When the coolant reaches a specified temperature, the thermostat opens and coolant flows through the upper hose to the radiator. While flowing through the radiator tubes, the coolant heated by the engine is cooled by the airflow across the radiator while the vehicle is moving. If the airflow is not sufficient to maintain the specified engine temperature, the electric cooling fan is activated. The cooled coolant flows to the lower radiator tank, from where it returns to the water pump and the cycle repeats.

When the engine reaches normal operating temperature, the coolant expands and part of it is forced out of the cooling system through the radiator cap pressure valve into the reserve tank. When the system cools, coolant from the reserve tank returns to the system through the radiator cap vacuum valve. The reserve tank is not sealed and is not pressurized.

The electric cooling fan is mounted on the back side of the radiator. When the coolant reaches a specified temperature, the contacts of the temperature sensor close and the fan is activated through a relay.

Warning: Avoid getting antifreeze on your skin and on painted surfaces of the vehicle. If this occurs, flush the antifreeze off with plenty of water.

Warning: When working on models equipped with air conditioning, observe safety precautions.