1999 Audi A4 overheating

Use only coolant additive G 12 meeting specification VW 774 D. G 12 coolant is red in color. G 12 must not be mixed with any other additives. If the fluid in the expansion tank is brown, this is an indication that G 12 has been mixed with another type of coolant. In this case the coolant must be changed. Also, if radiator, heat exchanger (heater core), cylinder head or cylinder head gasket, have been replaced, flush cooling system and replace engine coolant.
G12 coolant additive may be used in older vehicles when original coolant is drained and cooling system is flushed. Contaminated coolant must be drained immediately and cooling system flushed.

To fill without using special tools, loosen coolant expansion tank and lift about 4" (100 mm). Remove grommet holding clip at heater core and pull back grommet. Loosen coolant hose on heater core and pull back hose sufficiently so that bleeder hole is no longer sealed by connection. See Fig.
Add coolant until it flows out of coolant hose bleeder hole. Push coolant hose on connection and tighten. Install coolant expansion tank cap.
Start engine, and raise engine speed to 2000 RPM for approximately 3 minutes. Allow engine to idle, until lower radiator hose is hot. Check coolant level, and top off if necessary. When engine is at normal operating temperature, coolant level must be at MAX mark on expansion tank. When engine is cold, coolant level must be between MIN and MAX marks, on expansion tank.