Draining the coolant
To drain the coolant, disconnect the lower radiator hose. On models with 1.1/1.3 L engines, disconnect the lower hose from the lower branch pipe of the main pipe at the engine. On models with 1.5/1.6/1.8 L engines, disconnect the hose from the lower branch pipe of the cooling pump. The heater valve must be open.
Before disconnecting the hose, make sure the system is not under pressure. Remove the radiator cap (or the expansion tank cap) and release the pressure in the system. If the engine is hot, take precautions to avoid scalding.
If you leave your car without coolant, attach a note to it to prevent someone from accidentally starting the engine.
Filling the system
Never use pure water in the cooling system, as this will lead to intensive corrosion of the parts. To prevent corrosion and scale formation, use an all-season antifreeze with corrosion inhibitors (see chapter "Car maintenance work"). In summer, you can use water with added corrosion inhibitor.
Reconnect the lower radiator hose. Check the other hose connections for tightness, especially if they have been disconnected. Mix a solution of antifreeze or rust inhibitor in distilled water according to the manufacturer's instructions and pour coolant into the system. Pour the coolant slowly to avoid air locks. Run the engine for a few minutes with the radiator cap open to release any remaining air in the system.
Check the coolant level in the radiator filler neck or in the expansion tank and add fluid up to the "MAX" mark.
After several minutes of engine operation, the fluid level may decrease due to the removal of residual air from the system. Add fluid up to the "MAX" mark.
(The original text is available on the portal: VWMANUAL.ru)
Flushing the cooling system
If the engine frequently overheats without any obvious cause, it is possible that the cooling system is clogged internally with scale, rust and dirt deposits. In this case, the cooling system must be flushed.
It is recommended to first treat the cooling system with a special agent (solvent) for flushing radiators - even if the system is not completely cleaned, the solvent will soften internal deposits and facilitate further flushing.
If the system is not completely cleaned with solvent, flush it with high-pressure water. It is best to direct the water flow during flushing in the opposite direction to the fluid flow during normal engine operation.
To back flush the entire system, disconnect the hose from the rear of the cylinder head and insert a hose into the fitting and run high pressure water through it into the engine cooling jacket.
In case of severe clogging of the system, its elements (radiator, heater, engine jacket) can be flushed separately. The radiator for flushing must be removed from the car, the radiator cap installed and turned upside down, and then flushed under pressure by inserting a hose into the lower branch pipe.
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