Author: pawel

Coolant replacement – Golf 4 and Bora:

1. By slowly unscrewing the cover of the expansion tank, reduce the pressure in the cooling system. Be careful with a hot engine, there is a risk of scalding by the coolant.

2. Remove the noise canceling cover under the motor and prepare a suitable vessel. Under no circumstances may the coolant be drained onto the ground.

3. Unscrew the coolant drain valve at the bottom of the radiator (gasoline engines 1,4 i 1,6 l). In gasoline engines 1,8 l and in diesel engines 1,9 TDI, to drain the liquid, additionally disconnect the oil cooler hose.

4. So that the liquid drains better, remove the cover of the expansion tank. Drain the liquid into the vessel.

5. Tighten the drain valve before refilling the system.

6. Pour coolant slowly into the expansion tank, until no more air bubbles come to the surface.

7. Screw in the cover of the expansion tank.

8. Start the engine and let it idle for approximately two minutes. Then increase the speed to approx. 1500 rpm and top up with coolant to the overflow hole in the expansion tank.

9. Check the coolant level. The level should be up to the MIN marking when the engine is cold, and if the engine is hot, the MAX markings.

Checking the tightness of the cooling system:

1. Check that the hoses leading to the radiator, engine and heater are tight.

2. Check the condition of flexible hoses by crushing them. If they are stiff, brittle or cracked, they must be replaced with new ones.

3. Check that the hoses are well seated on the connectors.

4. The screws of the cable clamps should be tightened. They may have become loose during driving and under the influence of pressure in the system. Replace corroded bands with new ones.

Checking and topping up the coolant level:

The coolant level should be between the MIN and MAX marks. A much higher or lower level indicates a system fault, the cause of which must be determined. If the engine is hot, carefully loosen the expansion tank cover by one turn. There is a danger of steam spraying out. For safety, unscrew the cover through the cloth.
1. Check the coolant level with the engine cold, because then there is no excess pressure in the system.

2. With the engine cold, the coolant level in the expansion tank should be between the MAX and MIN markings. remember, that the liquid level is always higher when the engine is hot. Do not be influenced by the possible indication above the MAX.

3. To refill the liquid, unscrew the tank cover. When the engine is hot, use a thick rag and unscrew the cover slowly and carefully to relieve pressure in the system.. Opening the lid too quickly will cause hot liquid to squirt out of the tank.

4. Never add liquid above the MAX level. The liquid expands at high temperature and its excess escapes to the outside of the system.

5. You can fill in small fluid losses with a cold or hot engine.

The cooling system is to ensure the proper operating temperature of the engine. It includes a cooler, thermostat, flexible hoses and a network of channels in the block and engine head with precisely selected cross-sections, in which the coolant flows. This creates a protective coat, which collects the heat of combustion and conducts hot liquid through the pipes and channels to the radiator. The coolant circuit depends on the engine temperature.

Coolant circuit

After starting a cold engine, the coolant circulates in a small circuit, covering only the engine and heating. In this circuit, the path to the radiator is blocked by a thermostat. The coolant returns directly to the engine and heats up quickly, which in turn allows you to quickly reach the correct operating temperature of the engine. Only after the liquid has reached a certain temperature, a cooler is turned on in the circuit. The thermostat opens the way to it and the cold liquid remaining in the radiator mixes with the already hot liquid from the short circuit. The mixing of the liquid is necessary to avoid the so-called. thermal shock of the engine.

With increasing coolant temperature, The thermostat opens the way to the radiator more and more and at the same time closes the shorter cycle. When the engine operating temperature is reached, liquid flowing from the bottom, cold exhaust line in the radiator enters the pump, which presses it to the engine block and cylinder head. From there, most of the liquid is routed through an open thermostat to the radiator, and the rest to the heat exchanger (heater) heating system. The cold liquid flowing out of the cooler makes room for the hot liquid, which is cooling down, flowing through the radiator fins, while driving, the engine temperature drops below a certain value, the thermostat shuts off the flow of coolant to the radiator pending, until the engine reaches the required operating temperature.

attention: Coolant circuit, thus, the routing of the lines in the cooling system is adapted to the particular engine. The figures below show simplified examples of solutions in the most popular engines.

Fluid pressure and fan

At normal engine operating temperature, there is an overpressure in the cooling system from 0,14 do 0.16 MPa. As a result, and due to various additives to the coolant, its boiling point is raised from 100 ° C to about 120 ° C. Higher engine operating temperature means more economic operation and fuel savings. When the pressure in the cooling system exceeds when the engine is hot 0,15 MPa, then the pressure valve on the expansion tank opens, through which a little vapor of the cooling liquid flows out. Despite this, the cooling system may overheat when driving around town. This is prevented by additional cooling of the radiator by means of a fan (one or more), which is controlled by a two-stage thermal switch. It is mounted on the left side of the radiator casing. At a coolant temperature of 92…97° C the first stage is turned on (half the speed). At a temperature of 99…105° C the thermal switch switches the second stage on (full fan speed). The fan is turned on periodically and the coolant circuit controlled by the thermostat allows the engine to work at the correct operating temperature, thus saving fuel.

Cooling liquid

The coolant is a mixture of water and anti-corrosion and anti-freeze agents. The anti-corrosion additive prevents scale build-up in the cooling system and the formation of rust spots. This additive loses its properties after approximately four years and the coolant must be replaced after this period. Volkswagen does not order the fluid to be changed regularly. Depending on the antifreeze used, the proportion of water in the coolant is up to 60%. These proportions should not be different also in summer.

All engines use a new reddish water and red G12 coolant, prepared according to the TL VW factory standard 774 D. This liquid must not be mixed with the previously used G agent 011 A8 C to protect against corrosion and freezing of liquids, as this can seriously damage the engine. The change in color of the liquid to brown is indicative of this, however, there was a mixture of the two types of protective measures. In this case, completely drain the cooling system, rinse it with water (run the engine for two minutes) and fill with new liquid.