Interesting...I got a call a while back from the A8/R8 division, in reply to an email I sent about another "concern" (the faulty oil cooler coolant pipe installed on all D2's and maybe D3's?). While I had them on the line, I questioned the thermostat problem. He said that they were not aware of any such problem and that statistically, Audi A8 units did not fail any more often than other luxury brands.
He further told me that my coolant system was obviously contaminated, otherwise I couldn't be on my 3rd thermostat in 100K miles. So, I was urged to get my car to an authorized Audi Dealer as soon as possible for a full inspection and chemical flush.

This "advice", incidentally, came from the same person who had just prompted me to describe the location of the oil cooler, how it functioned and why it would have a coolant pipe involved. A call center employee reading from a script.
He said he would pass my concern on to the engineering dept, but also commented that since my car was "old", I had to expect things to go wrong.

I'd have been better off spending that time picking my nose or taking a short nap

 

They just tell you what you want to hear to make you feel better about your product. lol @ chemical flush or whatever crap they try to sell you.

 

I have R&Red about 20 D3 BFM thermostats. Both with genuine and Wahler units. Both fail, average mileage is about 30k. Leading me to believe it has nothing to do with the thermostat. Every 5v V motor Audi has uses the same style thermostat from the 2.8 AHA up to the 4.2 BFM. I never seen a properly maintained 5v V motor overheat due to a stuck thermostat. I have seen thermostat stick on vehicles that are 10 years old with low mileage and vehicles that are way overdue for a timing belt job. But nothing like the BFM engine in the A8. I have talked to Audi Master Guild technicians with 30 years experience, Audi Technical Field Managers, and Audi Training Instructors and everyone agrees it must have something to do with heat transfer of the BFM block. Just my two cent. Is that the answer, I don't know.

 

"I never seen a properly maintained 5v V motor overheat due to a stuck thermostat. I have seen thermostat stick on vehicles that are 10 years old with low mileage and vehicles that are way overdue for a timing belt" ???

A little puzzled by that statement ^^^ Mine is an always meticulously maintained '01 D2 AUX motor...first thermostat change under warranty by Audi dealer at about 45K miles, stuck closed and overheating. Next was by me before 100K miles...stuck closed and overheating...tested in boiling water, stuck closed. Bad therm was clean as a whistle, even under heavy magnification...no visible corrosion or cracks...nothin.

D2-only forums touch on this constantly and the general consensus is 30-50K miles...almost guaranteed, just like the badly designed prop shaft flange seal (even more often sometimes).

 

You're out of your mind, maybe its too cold in the area you live in but i have changed thermostats in 2.8, 2.7, 3.0, 4.2, engines hundreds of times before the 100k mark. I would almost say the 2.8L as much as the 4.2, ALL of them stuck closed.
Another point is the AMB 1.8T engines (B6) which has the thermostat in a entire plastic housing outside the engine under the intake manifold also tends to stick closed at or around the 100k mark, and those you have to buy the entire damn housing with it.

Just saying.......My best friend at my dealership (RIP, became CHP and killed) was master guild status and he would probably also come in to say that while the 4.2L thermostats do take a crap faster than the smaller engines, if it had a better designed T stat there wouldn't be a problem. I actually remember arguing with him about this and he said since the thermostat is closed while its warming up and heat was the cause of failure, it should actually stick open if the block were to blame, not closed.

I'll even give a link to honor him.
http://www.jarrodmartinez.com/

 

They do stick close, but many of my personal experiences go like this: I have a vehicle come in for a service, and after I perform the service I will take it for a road test. On the road test, I will notice the temp. gauge not going up to the mid-way mark, there to no and very little heat and then I bust out the VCDS and see the vehicle is not running at proper temp. I will check to see if the CTS is reading the same temp in 01 and 17, and if so, it's time to do a t-stat.

I have 4 engine jobs at my shop as I post and only one is from overheating.... And it was not the thermostat, it was the electric fans not coming on (98 Cabriolet) the others are snapped t-belts. I probably have done about 100 t-belt job in the past year, and I always change out the t-stats with that service, so I have not seen many non 4.2 t-stats stick closed? I do over see the service of about 400 Audi/VW a year, and I am a guru in my neck of the woods. Just saying