This article discusses the upper radiator coolant hose for the D2 Audi A8 (1997 through 2002) with the main focus being on the pricing.
The information herein is based on my set of 1998 Audi A8 D2 Quattro project cars. In these, the upper radiator coolant hose is a common point of failure.

Dealer pricing for this hose is expensive. Even though we have found an aftermarket supplier it is still the original equipment that is being offered and the prices still high, close to $200. The hose is fairly complex with a four-way junction that includes a small nipple, which goes up to the coolant overflow bottle. The classic failure pattern is that this nipple breaks off.

Many of the parts on the D2 Audi A8 are shared with other Audi models. The resultant economies of scale keep the prices low for such parts. Sadly, this particular coolant hose is an exception — it is used only on the early Audi A8 models. These cars were only sold in small volumes. For an aftermarket manufacturer to create a coolant hose for such a low volume application is not viable; the economies of scale simply aren`t there.

So, we are faced with three unpleasant options:

• We can scavenge for these parts used, knowing that whatever we find might be 20 years old.
  
• We can come up with a good engineering fix for the damaged nipples. Whatever we use has to stand up to high pressure and temperature, over many years, so tempting solutions like Shoe Goo aren`t viable.
  
• We spend the almost-$200 and buy a hose.
  

The shape of this hose is critical. If it extends out too much it can hit the fan. If this happens, a fan blade can be damaged, which in turn throws the fan out of balance, which in turn prematurely wears out the fan bearing, which costs much more than the coolant hose and is very hard to replace (we know, we did it).