All A4 and Passat models are filled with a mixture of water and special phosphate-free antifreeze/coolant at the factory. This antifreeze/coolant has corrosion inhibitors that prevent frost, the formation of chalk and also raise the boiling point of the water. A4 and Passat models up through model year 1996 are filled at the factory with a special antifreeze/coolant, known as 'G11', Part No. ZVW 237 102 or G 011 A8 C.
Beginning with the production run of July, 1996, a new type of antifreeze/coolant was introduced, and used in the production of 1997 and later models. This fluid is the G 12 A8D TL 774 D or G 012 A8 D and referred to as 'G12'. The G12 coolant is easily identified by its red color and is mixed with distilled water at a 50/50 ratio on all USA models and a 60/40 ratio for all Canadian models.
Engine coolant used during recent production:
The coolant reservoir/expansion tank is translucent. If the reservoir is clean, it can be checked without removing the cap. The reservoir has LOW and HIGH level marks. The coolant must be between the two marks when the engine is cold, and slightly above the high mark at normal operating temperature.
When removing the threaded pressure cap from the reservoir, loosen the cap slightly first. Do NOT attempt to remove it if the coolant temperature is greater than 100°F (38°C). If the coolant begins to hiss or boil, tighten the cap and wait for the engine to cool down.
Some models are equipped with a coolant level warning light on the dash that illuminates when the ignition key is initially turned on as a bulb check feature and under normal conditions turns off once the engine is started. If the coolant level drops below the minimum level when the engine is running, the coolant level warning light will be activated.
The coolant level warning light is a convenient feature, however if the system malfunctions such as having a stuck float the warning light could fail to activate and the engine could overheat resulting in severe mechanical damage. For this reason periodic inspection of the coolant level in the reservoir itself is highly recommended.
If the coolant level is mildly low, it can be adjusted to the proper level by adding small amounts of distilled water until the coolant reaches the MAX mark on the reservoir. If the coolant level is extremely low, it is recommended that a 50 / 50 mixture of coolant (make sure to use the same type of coolant that is in the vehicle) and distilled water be used to adjust the level in the reservoir. In extremely cold climates, a ratio of 60 percent antifreeze/coolant and 40 percent distilled water can be used to prevent freezing.
In large quantities, simply adding distilled water to the system can dilute the ratio of coolant to water, which reduces the cooling capabilities of the system, and in extreme cases, can cause freezing of the coolant if the vehicle is exposed to low temperatures. If the coolant freezes in the engine, the engine block can (and often times does) crack. To prevent the coolant mixture from freezing, avoid adding large quantities of distilled water to the system if it is low.