3S-FE Engine Cooling System Diagram; 3S-GE; 4S-FE. 1 - from the radiator; 2 - inlet pipe; 3 - thermostat; 4 - coolant pump; 5 - idle speed control valve; 6 - throttle body; 7 - from the heater; 8 - to the heater; 9 - outlet pipe; 10 - to the radiator; 11 - coolant bypass hose; 12 - oil cooler (if installed).
Cooling system diagram for 4A-FE engines; 7A-FE. 1 - thermostat; 2 - coolant inlet pipe; 3 - from the radiator; 4 - coolant outlet pipe; 5 - to the radiator; 6 - coolant pump; 7 - from the heater; 8 - to the heater. 9 - coolant supply pipe to the pump; 10 - from the throttle valve heater; 11 - to the throttle valve heater; 12 - radiator.
These engines use a closed-loop liquid cooling system with forced circulation of coolant and a thermostat with a bypass valve in the coolant inlet pipe.
The cooling system includes:
- cooling jacket (in the cylinder block and in the cylinder head),
- radiator,
- coolant pump,
- thermostat,
- electric cooling fan,
- connecting hoses
- and other elements.
Coolant, heated in the cooling jacket, is pumped by a liquid pump into the radiator, where it is cooled by a fan and the oncoming air flow that occurs when the car is moving. The coolant then returns to the cooling jacket with the help of a pump and cools the engine. The cooling jacket is a network of channels that pass through the spaces between the cylinder liners in the cylinder block and communicate with the channels in the block head. The movement of the liquid is organized in such a way as to ensure the most effective cooling of those engine elements that are most heated during its operation (in particular, the upper belt of the engine cylinders and combustion chambers).
Radiator
The radiator is located in the front part of the car and is designed to cool the coolant coming from the cooling jacket. The radiator consists of right and left tanks and a radiator core that connects the two tanks. The upper tank contains an inlet pipe through which the coolant comes from the cooling jacket, as well as a hose for bypassing excess coolant or steam. The lower tank of the radiator contains an outlet pipe for the coolant, through which it enters the coolant pump, as well as a drain cock through which the coolant is removed.
The radiator core has a number of finned tubes through which the coolant flows from the upper tank to the lower tank, as well as cooling fins for more efficient heat dissipation into the environment. The coolant, heated as it passes through the cooling jacket, is cooled in the radiator by the air flow sucked in by the electric fan, as well as the oncoming air flow that occurs when the car is moving.
Models with automatic transmission have a special cooler for the automatic transmission fluid, which is located in the lower radiator tank. An electrically driven fan is located behind the radiator, which facilitates the flow of air through the radiator. The fan only turns on when the coolant temperature reaches the operating value. This reduces the power consumption for the fan drive and prevents overcooling of the engine.
Radiator filler cap (radiator cap)
The radiator cap is a sealing type, it must seal the radiator and withstand the increased pressure that occurs as a result of thermal expansion of the coolant. Increased pressure in the radiator prevents the coolant from boiling even at temperatures above 100°C. The radiator cap has a steam (throwing off) valve and air valve (vacuum valve). At a coolant temperature of 110-120°C, the excess pressure inside the radiator caused by the thermal expansion of the liquid reaches 0.3-1.0 kg/cm², or 30-100 kPa. If this limit is exceeded, the steam valve opens under the action of pressure and the steam is removed through the steam pipe. The air valve opens under the action of the vacuum that forms inside the radiator after the engine is stopped and the coolant temperature drops. Opening this valve allows the coolant in the expansion tank to return to the cooling system.
Expansion tank
The expansion tank is designed to accumulate excess coolant volume, which is obtained as a result of its volumetric expansion during heating. When the coolant temperature drops, it returns from the expansion tank to the radiator. Thus, the radiator is always filled with coolant, and unnecessary losses are prevented. To make sure that it is necessary to top up the coolant, it is necessary to check its level in the expansion tank.
Coolant pump
The coolant pump provides forced circulation of coolant through the cooling system. It is mounted at the front of the cylinder block and is driven from the crankshaft by the V-belt of the alternator drive.
Thermostat
The thermostat is installed on the inlet pipe of the cooling circuit. It has a wax bypass valve and an automatic valve controlled depending on the coolant temperature. The automatic valve closes when the coolant temperature drops, and thus prevents the liquid from circulating through the engine, accelerating the process of its warming up. At the same time, the bypass valve opens when the automatic valve closes, then the coolant circulates only inside the engine (on the small circuit of the cooling system). When the coolant temperature rises, the automatic thermostat valve opens and the bypass valve (if it is installed) closes, allowing coolant to circulate through the radiator.
The wax filler inside the thermostat power element expands when heated and cools when cooled. Heating the wax filler in the power element creates a force that overcomes the force of the spring, which holds the valve closed, thus opening the automatic valve. When the wax filler cools, it contracts, and under the force of the spring, the automatic valve closes. In these engine models, the thermostat maintains the operating temperature of the coolant at about 82°C.