All models of vehicles discussed in this manual are equipped with a positive pressure engine cooling system with thermostatically controlled circulation of the working fluid. The water pump of the rotary type is fixed on the engine block and provides pumping of the coolant through the cooling path of the latter. The flow of fluid washes the areas where each of the cylinders in the block is located and is directed to the rear of the engine. Cast-in-the-block and cylinder-head cooling ducts provide intensive cooling for intake and exhaust ports, spark plug areas and exhaust valve guides.
The wax-filled thermostat controls the operating temperature of the engine during engine warm-up. In the first minutes after starting a cold engine, the thermostat remains closed, thereby preventing the circulation of coolant through the radiator. When the engine temperature reaches normal operating temperature, the thermostat valve opens, connecting a radiator to the cooling circuit, ensuring maximum heat removal from the working fluid (coolant).
The cooling system is hermetically sealed and tightly sealed with a radiator cap capable of withstanding a certain overpressure, which increases the boiling point of the coolant and, accordingly, the efficiency of heat removal through the radiator. When the internal pressure in the system exceeds a certain value, the spring-loaded plate of the safety valve mounted in the radiator cap rises above its seat, ensuring that excess coolant flows through the connecting (overflow) tube into the expansion tank. As the system cools down, the fluid automatically returns from the reservoir to the radiator.
Coolant is added to the system through the neck of the expansion tank, which at the same time also acts as a receiver that accumulates excess liquid displaced from the radiator.
In view of the above design features, such a cooling system is called closed, since it excludes any functional loss of coolant.