1.1. Cooling system circuit of 1.2 l petrol engines 1. Expansion tank; 2. Coolant circulation pump "V50"; 3. Coolant pump; 4. Intercooler, in the intake manifold; 5. Heater radiator; 6. Thermostat housing; 7, 14. Non-return valve, in the coolant hose, not visible from the outside; 8. Throttle, in the coolant hose, not visible from the outside; 9. Radiator, combined with radiator 11; 10. Tour bocompressor; 11. Low-temperature radiator of the supercharging system, combined with radiator 9; 12. Cylinder head and block; 13. Oil cooler; 15. Additional heater, if available
1.2. Cooling system circuit of 1.4 l petrol engines Light outline. Engine cooling system coolant lines. Dark outline. Intercooler coolant lines. 1. Expansion tank; 2. Coolant circulation pump "V50"; 3. Intercooler, in the intake manifold; 4. Non-return valve, in the coolant hose, not visible from the outside; 5. Heater radiator; 6. Thermostat housing; 7. Throttle, in the coolant hose, not visible from the outside; 8. Oil cooler; 9. Radiator; 10. Additional radiator for intercooler; 11. Turbocharger; 12. Cylinder head and block; 13. Additional heater, if available; 14. Coolant pump
1.3. Cooling system circuit of 1.8 l petrol engines 1. Radiator; 2. Coolant circulation pump "V51"; 3. Coolant pump; 4. Thermostat; 5. Oil cooler; 6. Cylinder head and block; 7. Turbocharger; 8. Expansion tank; 9. To the additional heater; 10. From additional heater; 11. Heater radiator; 12. Connecting coolant lines
1.4. Cooling system circuit of 2.0 l diesel engines (CFHC, CFJA, CLCB) 1. Expansion tank; 2. EGR radiator, after replacement, replace the coolant; 3. To the additional heater; 4. From the additional heater; 5. Cylinder block, after replacement, replace the coolant; 6. Heater radiator, after replacement, replace the coolant; 7. Throttle, in the coolant hose, not visible from the outside; 8. DSG fluid radiator; 9. Regulator; 10. Oil cooler, after replacement replace the coolant; 11. Coolant circulation pump No. 2 "V178"; 12. Radiator, after replacement replace the coolant; 13. Sensor "G83" coolant temperature at the radiator outlet; 14. 4/2-way valve, with thermostat; 15. Coolant pump; 16. Cylinder head
The engine cooling system operates according to the following algorithm. Until the engine is warmed up, the coolant (coolant) is pumped by a water pump only in the cylinder head and block, as well as in the interior heater heat exchanger. This way the engine warms up quickly. When the coolant temperature rises to a certain value (controlled by ECT sensor) the thermostat opens a large cooling circuit and the coolant circulates additionally through the radiator, being cooled by the air passing through it. In this way, the engine's operating temperature is maintained. When the coolant temperature reaches an even higher value, the cooling system fan turns on, which begins to create an additional air flow through the radiator fins for more intensive heat removal from it.
In addition to the heater radiator, the cooling system circuit may include an oil cooler (see Chapter 2), additional heater radiator (if available, see Part B), dSG fluid radiator (on models with DSG, see Chapter 7), radiator for intercooler (on petrol models 1.2 and 1.4 l, see Chapter 4) and EGR cooler (on diesel models, see Chapter 4).
The coolant pump, or water pump, is driven by:
- on petrol models 1.2 and 1.4 l - auxiliary drive belt;
- on 1.8 l petrol models - a separate toothed belt from the balance shaft;
- on diesel engines - from the crankshaft via the timing belt.
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The electric coolant circulation pump "V50" or "V51" is responsible for the circulation of coolant when additional functions are enabled, for example: using residual heat to warm up the interior and pumping coolant after the engine is turned off.
The residual heat utilization function allows you to maintain the required temperature in the car interior when the engine is off, as long as the coolant temperature remains high enough. To do this, the circulation pump, in response to commands from the engine control unit, maintains the flow in the cooling system circuit. If there is not enough residual heat, the climate control unit switches off the residual heat function. Pumping coolant after turning off the engine is a protective function of the engine. This method prevents the formation of vapor in the cylinder head areas after the engine is turned off. The function is activated if, after the engine is switched off, the coolant temperature exceeds 105°C and the vehicle was driven with a correspondingly high load in the previous driving cycle.
Precautionary measures
Before working in the engine compartment, especially in the radiator fan area, be sure to disconnect the negative battery cable and the fan wiring connector, as it may turn on due to thermal conductivity even when the ignition is off.
Do not open the coolant expansion tank cap until the engine has completely cooled down to avoid being burned by hot liquid or its steam.
If you need to open the expansion tank cap when the engine is hot, wrap it with a rag. Unscrew the cap slowly, gradually reducing the steam pressure.