Ask any old mechanic and they'll tell you about the 'Italian tune up,' which involves driving a car really hard as a means of maintenance. Not only is this actually true (not just a line mechanics feed dumb millionaires so they can thrash their Lamborghinis), it applies to a number of non-Italian cars. Just head over to r/JustRolledIntoTheShop and take a look at the carbon buildup on this V10-powered 2007 Audi S6.
Check out the original thread detailing the full damage right here on Reddit, posted by the brilliantly-named user HowdyAudi. The comments there have a lot of great discussions on what's going on specifically with this engine on a technical level. I'll give you the abridged version.
Here's the damage.
That's a lot if carbon buildup!
Here's the view into the engine itself.
And here's even a look at the back of a valve.
HowdyAudi said that surprisingly, the engine didn't run that rough, but the check engine light was on, and that carbon buildup in other high-strung Audis (particularly the V8 RS4) can hang open the valves enough to cause misfires.
Why has this happened? Well, there are a few reasons. Initially, people in the thread started asking about exhaust gas recirculation, where some of the exhaust is piped back into the cylinder to keep combustion temperatures low and thus preventing too much nitrogen oxide from forming. It's an emissions compliance trick, but HowdyAudi explains EGR is not the culprit here.
This is an 07 Audi S6. So no EGR. They use a secondary air. Air pump and valves into the exhaust ports. This buildup is due, in my opinion, to excessive oil vapor and no fuel wash on the back of the valves.
This is a direct injection engine. That means that a normal engine would clean the back of its valves as fuel runs down into the cylinder. Direct injection shoots fuel right into the cylinder and skips the valves. It's efficient, but you miss out on the whole self-cleaning thing.
Another commenter asked why there was excessive oil vapor. Were crankcase pressures getting too high? Was a broken positive crankcase venting valve at fault? HowdyAudi explained once more.
All of the above. One thing I have found working on Audi's for years is they seem to not be able to figure out breather systems very well. Every model seems to have problems. This one did have a bad crankcase breather valve/oil separator that was replaced a while back. Plus this has almost 150000 miles on it. There was nearly 1/4 quart of oil in the intake manifold.
It was at this point that people started asking what could be done to prevent this kind of buildup. The answer was simple: drive harder.
One person said it looked like the owner probably rarely took the engine anywhere near redline. HowdyAudi elaborated.
I think that has a lot to do with it. Especially if you just sit on the freeway and idle all the time. Stop and go. These cars really do need a good flogging often.
Driving them hard will help. Freeway miles. Making sure it gets warmed up. I also recommend a product from BG, called MOA. Put it in the oil every oil change.
After all this, HowdyAudi had to scrape out the buildup with picks and pipe cleaners and clean with chemicals.
I used BG ISC cleaner. Really nasty stuff. Scrape out as much carbon as you can with picks and brushes. Then pour the ISC in. Keep scraping and brushing. Let is soak for 15 minutes or so. Clean it out. Wipe out the gunk. Give it another rinse with the ISC, brake clean. I spend about 30 minutes per port. So 5 hours of cleaning with 10 intake ports.
This is all to say that thrashing your car will not keep you from any kind of problem. As HowdyAudi went on to say, carbon buildup is "the nature of the beast" with these cars, and you'll need to deal with all of this at some point.
But some high-strung engines just need their legs stretched. The only question remains is, as HowdyAudi asked, with 435hp and 396 lb-ft of torque, where exactly can you legally run this car flat out?
Photo Credits: Audi (top), HowdyAudi (all others). You can check out the full Imgur galleries of this cleanup right here and right here for his dive into the S6's busted and oil-filled intake manifold.
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