Cooling System: Description and Operation
The cooling system consists of the radiator cap, radiator, coolant reservoir, hoses, water pump, cooling fan, and thermostat. The radiator is of tube-and-fin type.COOLING SYSTEM CIRCULATION
1. While the engine is warmed up (thermostat closed), coolant circulates as follows.
2. When coolant is warmed up to normal temperature and the thermostat opens, coolant passes through the radiator core to be cooled as well as the above flow circuit.
RADIATOR CAP
A pressure-vent cap is used on the radiator. The cap contains a pressure valve and ventilation valve.
The pressure valve is held against its seat by a spring of predetermined strength which protects the cooling system by relieving the pressure if the pressure in cooling system rises by 90 kPa (12.8 psi).
The ventilation valve operates as follows.
- It opens to let the air out of the radiator when the temperature and the pressure in the radiator are lower than ventilation valve weight.
- It closes when the engine has warmed up and the pressure in the radiator has risen.
- It opens when the engine has cooled after being warmed up once and vacuum has occurred in the radiator so as to prevent the coolant level in the radiator from falling and the radiator from being collapsed due to the vacuum in it.
NOTE: Do not remove radiator cap to check engine coolant level; check coolant visually at the see-through coolant reservoir.
Coolant should be added only to reservoir as necessary.
WARNING: As long as there is pressure in the cooling system, the temperature can be considerably higher than the boiling temperature of the solution in the radiator without causing the solution to boil. Removal of the radiator cap while engine is hot and pressure is high will cause the solution to boil instantaneously and possibly with explosive force, spewing the solution over engine, fenders and person removing cap. If the solution contains flammable anti-freeze such as alcohol (not recommended for use at any time), there is also the possibility of causing a serious fire.
COOLANT RESERVOIR
A "see-through" plastic reservoir is connected to the radiator by a hose. As the vehicle is driven, the coolant is heated and expands. The portion of the coolant displaced by this expansion flows from the radiator into the reservoir.
When the vehicle is stopped and the coolant cools and contracts, the displaced coolant is drawn back into the radiator by vacuum.
Thus, the radiator is kept filled with coolant to the desired level at all times, resulting in increased cooling efficiency. Coolant level should be between "FULL" and "LOW" marks on the reservoir.
Coolant should be added only to the reservoir as necessary.
NOTE:
^ Be sure to check cap gasket is located as shown figure and breather hole is not plugged.
^ When installing reservoir cap, align arrow marks on the reservoir and cap.
WATER PUMP
The centrifugal type water pump is used in the cooling system. The pump impeller is supported by a totally sealed bearing. The water pump can not be disassembled.
THERMOSTAT
A wax pellet type thermostat is used in the coolant outlet passage to control the flow of engine coolant, to provide fast engine warm up and to regulate coolant temperatures.
A wax pellet element is hermetically contained in a metal case, and expands when heated and contracts when cooled.
When the pellet is heated and expands, the metal case pushes down the valve to open it.
As the pellet is cooled, the contraction allows the spring to close the valve.
Thus, the valve remains closed while the coolant is cold, preventing circulation of coolant through the radiator.
At this point, coolant is allowed to circulate only throughout the engine to warm it quickly and evenly.
As the engine warms, the pellet expands and the thermostat valve opens, permitting coolant to flow through the radiator. In the top portion of the thermostat, an air bleed valve is provided; this valve is for venting out the gas or air, if any, that is accumulated in the circuit.
COOLANT (WATER) TEMPERATURE SENSOR
The Engine Coolant Temperature (ECT) sensor is located at water outlet cap. This gauge activates a temperature meter gauge in the instrument cluster.
When installing, wind sealing tape on gauge thread and tighten it.
COOLING FAN CLUTCH
Fluid is enclosed in the cooling fan clutch and at its center front, there is a bimetal whose thermal reaction and the engine speed control the cooling fan speed.
The clutch is installed to the cooling fan pulley, so that the cooling fan operates at approximately the same speed as the water pump shaft regardless of the air temperature at the front of the clutch when the water pump shaft turns at low speed (when the engine running at idle speed).
The relation between the temperature detected by the fan clutch and operation of the fan clutch is as follows.
While the fan clutch detects a temperature lower than 50°C, it remains OFF and the fan revolution speed is constant (500 to 800 r/min. (rpm))regardless of the engine speed. As the temperature reaches 50°C to 70°C, the fan clutch turns ON gradually and the fan revolution speed increases.
A temperature exceeding 70°C causes the fan clutch to turn ON and the fan revolution speed to increase in proportion with the engine speed.
Once the engine speed exceeds 4,000 r/min. (rpm), however, the fan revolution speed becomes constant (2,250 to 2,550 r/min. (rpm)).
NOTE: Do not disassemble fan clutch.