Coolant circulation

Coolant circulation is continuously maintained by a coolant pump. While the engine is cold, coolant circulates only in the engine head and cylinder block and in the heat exchanger. When the coolant is heated, the thermostat opens a large circle of circulation and a constantly running pump directs the liquid through the radiator. The coolant flows through the radiator from top to bottom and is cooled by the air flow passing through the radiator fins, which occurs when the car is moving.

When the coolant temperature is high, the electric fan turns on, which provides additional cooling to the radiator. The electric fan is turned on and off as needed by a thermal switch. Depending on the equipment, for example, in the presence of an air conditioning system, an additional electric fan is installed.

Safety instructions

The electric fan can turn on automatically even when the ignition is off. Due to the heat back-up in the engine compartment, repeated switching on is possible. Before working in the engine compartment, disconnect the plug at the blower motor.

Caution: When working on the cooling system, make sure that coolant does not come into contact with the toothed belt under any circumstances. The glycol contained in the coolant can damage the cord of the toothed belt so that after some time in operation the belt will break and this will lead to severe engine damage.

Note: Lay the coolant hoses stress-free during installation so that they do not come into contact with other parts. If there are marks or arrows on the pipelines and the ends of the coolant hoses, they must be opposite each other during installation.

Dual-circuit cooling system for a gasoline engine with a displacement of 1.4 liters and direct injection of gasoline

The FSI engine has a dual-circuit cooling system. In this case, separate coolant flows with different temperatures are directed through the cylinder head and cylinder block. Coolant flow is controlled by two thermostats located in a common housing. One thermostat is for the cylinder block and the other is for the cylinder head.

The double-circuit cooling system has the following advantages:

• The cylinder block warms up faster because the coolant stays in the block until it reaches 105°C.
• Due to the higher temperature level of the cylinder block, friction in the crank mechanism is reduced.
• Better cooling of the combustion chambers due to lower cylinder head temperatures.