1 – coolant supply hose to the heater radiator; 2 – coolant drain hose from the heater radiator; 3 – heater tap; 4 – heater radiator; 5 – liquid drain tube; 6 – coolant drain hose from the intake pipe; 7 – expansion tank; 8 – radiator supply hose; 9 – radiator cap; 10 – Upper radiator tank; 11 – radiator pipe; 12 – electric fan; 13 – lower radiator tank; 14 – radiator drain hose; 15 – coolant pump; 16 – coolant supply hose to the pump; 17 – thermostat; 18 – thermostat bypass hose.
Position of thermostat valves at different coolant temperatures
I – from the cylinder head; II – to the coolant pump; III – from the lower radiator pipe; 1 – main valve, 2 – bypass valve.
The engine cooling system is a liquid, closed type with forced circulation. When the engine is cold, the liquid circulates in a "small circle". It includes the cooling jackets of the engine block and cylinder head, the coolant pump, the thermostat, and the heater radiator when its valve is open. When the liquid temperature reaches 80–85°, two thermostat valves are activated, blocking the small circle and opening the path for the liquid through the engine radiator, which is intensively blown by the oncoming air flow when driving, as well as by an electric fan.
The radiator consists of two horizontal tanks connected by tubes. For better heat dissipation, plates are pressed onto them. Liquid is supplied to the radiator through the upper branch pipe and is discharged through the lower one.
Passing through the radiator, the liquid cools down, after which it enters the engine again. The expansion tank compensates for the change in the volume of the coolant when it is heated or cooled. For visual control of the coolant level, the tank is made of translucent polyethylene.
The tightness of the system is ensured by the inlet and outlet valves of the radiator filler cap. When the engine is hot, the outlet valve maintains increased pressure in the system. Due to this, the boiling point of the liquid increases. When it cools down, the inlet valve opens, passing some of the liquid from the expansion tank to the radiator and thereby compensating for the decrease in the volume of liquid.
There is a hole in the expansion tank cap, so the pressure in its internal cavity is always atmospheric.
The coolant pump is of the centrifugal type. The pump body is aluminum, disassemblable, consists of two parts. The pump shaft rotates in a double-row sealed bearing that does not require maintenance. The flange of the pump drive pulley is pressed onto the front end of the shaft - a V-belt from the engine crankshaft pulley.
Recently, cars have been equipped with radiators with plastic tanks and an aluminum core.
It is not recommended to pour water into the engine cooling system. This leads to scale formation on the system walls, corrosion of parts, deterioration of heat exchange and reduction of the pump seal service life.