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Re: Octane vs. carbon buildup?

The later may be more accurate.  Audi knew of the carbon build up as early 
as March 1996 when they issued a Technical Bulletin regarding the 
problem.  I bought my A6 in July 1996.  Interesting thing is that there are 
literally millions of cars on the road that do not suffer aforementioned 
problem, and the A6 engine is not stressed at all within the parameters 
they work with.  In my opinion Audi is counting on most of their customers 
being ignorant and insensitive to unexplained noises.  Than the warranty is 
over and it is your baby now.  In all fairness to Audi, I have heard that 
they have picked up tabs on carbon removal with vehicles way out of 
warranty period.

At 10:23 AM 10/20/99 -0700, you wrote:
>Thanks for the info.  Seeing as you've taken complete care of your car, 
>it's really surprising this happened.  Interesting to know too that 
>premium gas didn't help\prevent this.  So Audi is clueless as to the 
>cause?  Or maybe they just want to keep the lid on it?
>>From: "Milan B. Milojevic" <milanb@earthlink.net>
>>To: "The Stevens" <the_stevens@hotmail.com>
>>CC: quattro@audifans.com
>>Subject: Re: Octane vs. carbon buildup?
>>Date: Tue, 19 Oct 1999 20:09:13 -0700
> From day one I have used 92 octane from Chevron, 76 Union and
>>Mobil.  Nothing else was ever used.  I have also changed oil on a regular
>>3,500 mile intervals (Castroll 20W50W).  All services were done on time by
>>the dealer, as well as the oil changes, from which I have purchased the
>>vehicle.  We have, what I consider, a good relationship.  You can well
>>imagine my surprise at AudiUSA authorizing engine removal and disassembly
>>to locate the source of the knock that occurred only when starting the car
>>cold (for Southern California).  The noise only lasted a few seconds and
>>was gone.  The condition was intermittent. There was no oil usage, the
>>mileage was within the specs.  There was no lack of power nor any
>>pinging.  In another words there was nothing to indicate excessive carbon
>>build up.  Dealer's diagnostic equipment also indicated no
>>problems.  Emissions were fine. Once the engine was opened it was like
>>opening a Pandora's box.  There were mechanical problems on top of the
>>carbon build up.  I won't go into those right now, but suffice to say that
>>they were severe enough to warrant a factory rebuild engine.
>>In my limited technical opinion there should have been some signs to
>>suggest carbon build up.  There should have been some sort of signal from
>>O2 sensor indicating incomplete combustion.  NOX sensor also should have
>>indicated something.  The realities of what we found once the engine was
>>opened did not correlate to the information that the on board computers
>>were showing.  Maybe someone more knowledgeable than me could explain all 
>>With all of the above problems I still belive in the Audi product and would
>>love to own a new one with 5 valve head geometry.  So far I have not seen
>>any reports on the carbon build up in those engines.  Does anyone know if
>>the new A6 and, or new A8 suffer from the similar faith.  Currently Audi's
>>solution is to have regular chemical carbon removal and fuel
>>additives.  This increases operating cost of the vehicle, not to speak of
>>the inconvenience.
>>At 11:55 AM 10/19/99 -0700, you wrote:
>>>There may be no correlation, but I am wondering what octane (rating system
>>>taken into account) level of gas is used by those who have had massive
>>>carbon buildup, and by those that haven't?
>>>I've always used 92 octane (Chevron, btw) in my VW\Audi cars, because of
>>>course with the higher compression they don't run too well on anything
>>>less than premium.  At least in my experience.
>>>What then is the current wisdom on keeping your valves, pistons and
>>>combustion chambers clean, besides Techron?  Does octane\quality of gas
>>>play a role?
>>>Also did Audi issue a TSB on why those A6s have the carbon problem as
>>>listed below?  Too cold a thermostat??
>>>AudiUSA just replaced my 1996 A6 engine at 49K for carbon build up and
>>>other mechanical problems.   I couldn't beleive the amount of carbon in the
>>>combustion chamber.  Anyway, when did you start using Audi Techron (milage
>>>wise)?  Is Audi Techron different from Chevron Techron, the inventor of the
>>>At 01:34 PM 10/18/99 -0700, you wrote:
>>>>I use the Audi Techron additive once a month and the inside of the engine
>>>>was clean at 287km when the head was pulled off. No carbon on the pistons,
>>>>or valves and I'm still running the original injectors. Can't hurt.
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