Audi Repair: radiater reserve tank, reservoir tanks, reserve tank

Question
i have a Audi a6 my reserve tank is no good. can i replace it with a Audi a4 tank.

Answer
What is a reserve tank?  The audi cars do not have reserve tanks.  Unless you mean coolant reservoir tanks, which depend on the engine that is fitted to the cars.  I would get a dealer to cross-reference the part numbers, if the same part number is used for both applications, then the parts are interchangeable.  Good luck,  Jan