Figure 3.79. Scheme of the engine cooling system: 1 - engine; 2 - radiator; 3 - expansion tank; 4 - heater radiator; 5 - thermostat housing; 6 - fitting for air removal; 7 - oil-water cooler (for vehicles with automatic transmission); 8 - thermostat; 9 - water pump
coolant hoses (K7J engine).
1 - Radiator, 2 - Cylinder head, 3 - Heater, 4 - Expansion tank.
The closed-type cooling system consists of the following main elements: a radiator located in front, an engine water jacket, a water pump, a timing belt-driven timing mechanism, an electric fan, a thermostat and connecting hoses. On vehicles with automatic transmission, a small additional radiator is installed. To compensate for thermal expansion and topping up the coolant, a separately located expansion tank is installed.
The thermostat valve opening temperature is 89°С, the temperature of the valve full opening is 101°С. Thermostat valve travel 7.5 mm. The pressure in the cooling system is 1.2 bar. The cooling system uses one 3-pin sensor, two of which are used to transmit information about the temperature of the coolant to the injection computer, and one for display in the instrument cluster. The injection computer controls the following depending on the coolant temperature:
- injection systems;
- engine cooling fan relay;
- signal lamp of the emergency temperature of the coolant, ignited at a temperature exceeding 118°C. The radiator fan is turned on by the fuel injection ECU at low speed if the coolant temperature exceeds 99°C, and turns off when it cools below 96°C. The high fan speed is switched on when the liquid temperature reaches 102°С, the high speed is switched off when the temperature is less than 98°С.
After the ignition is switched off, the injection computer enters control mode. If the coolant temperature exceeds 103°C within 5 minutes after the engine has stopped, the engine cooling fan low speed relay is energized. If the coolant temperature drops below 100°C, the fan relay is deactivated (fan operation time cannot exceed 12 minutes).
The cold coolant passes through the lower radiator hose to the water pump, which directs it to the cylinder block water jacket, passages in the block head, and the heater core. After cooling the block, combustion chambers and valve seats, the heated liquid enters the lower thermostat valve, which is closed until the liquid warms up, then to the heater radiator and again to the water pump. On a cold engine, coolant does not enter the main radiator, which helps the engine to warm up to operating temperature as soon as possible.
When the coolant reaches 89°C, a valve opens in the thermostat and the liquid enters the radiator, installed under the flow of incoming air in front of the car. The cooled liquid repeats the above cycle. If necessary (in hot weather, when driving at low speed) an electric fan is additionally switched on, which intensively cools the liquid.
The cooling system uses ethylene glycol based fluid - it is most suitable for systems with multi-metal components. Fluid should always be changed at the prescribed mileage interval. This is necessary not only to maintain its non-freezing properties, but also because over time, anti-corrosion additives lose their properties and metal oxidation products are formed in the cooling system, polluting it and worsening engine cooling.