The cooling system is sealed and consists of a radiator, water pump, thermostat, electric cooling fan, expansion tank and connecting hoses.
The system operates as follows. Cold coolant from the radiator passes through hoses and pipes to the water pump, which pumps coolant through the cylinder block and head. After the engine cylinders, combustion chamber and valve seats have cooled, the coolant enters the manifold and thermostat, which is initially closed, and is directed through the bypass hose back to the pump (Turbo models and with 2.0 liter fuel injection system) and/or to the heater, oil cooler and other related systems.
When the engine is cold, the thermostat is closed, the coolant circulates in a small circle. When the coolant reaches a certain temperature, the thermostat opens and coolant flows through the upper hose to the radiator. The coolant in the radiator is cooled by air when the car is moving. The air flow is enhanced by an electric cooling fan if necessary. Once the coolant reaches the other side of the radiator, the cycle repeats.
When the engine is at normal operating temperature, the coolant expands, some of it moving into the expansion tank. This coolant is collected in a reservoir and returned to the radiator when the system cools.
On T12 and early T72 models a vertical flow radiator is used, with upper and lower reservoirs; on later T72 models (since July 1987) A cross-flow radiator is used, which has reservoirs on the right and left.
The water pump is installed on the right side of the engine, driven from the crankshaft pulley through the drive belt. The cooling fan is mounted on the radiator and driven by an electric motor. It is controlled by a thermal switch and a relay. With a two-speed fan motor there is an additional relay and switch.
There are some differences between the cooling systems installed on different models. Automatic transmission vehicles have a radiator to cool the transmission fluid from below (or left) reservoir connected to the transmission by flexible hoses and pipes. Turbo and automatic transmission models have an engine oil cooler that is located at the rear of the cylinder block and connected to the main cooling system. On models with a 2.0 liter fuel injection system and Turbo, there is a connection between the cooling system and the throttle chamber.