http://jalopnik.com/here-s-why-the-v8-audi-s4-is-an-awful-used-car-1676466510
"As it turns out, there's a
reason these things have gotten so cheap. And given that this is a Volkswagen Group product, the reason is exactly what you'd expect: the engine has the propensity to blow up at any random moment, requiring a repair that costs approximately the same as one of those public art sculptures that always looks like a huge piece of discarded construction equipment, but actually symbolizes something like the struggle of the Asiatic Snapping Turtle against the tyrannical oppression of airplane noise.
Here's the background: the previous Audi S4, which came out in 1999, used a timing
belt rather than a timing
chain. This annoyed the hell out of everyone, because the belt had to be changed every few years, and the only way you can do this job, or
any job in a 1990s Audi, is you have to remove the front end, and the engine, and all the glass, and then you have to do a little jig on the service drive that involves a socket wrench and some lederhosen. For this, you may bill 31 hours.
So what Audi did on the V8-powered S4 model, which came out in 2004, was obvious: they ditched the stupid belt for a chain, like most other automakers. And since the chain was now designed to last the life of the car, Audi decided to stick it
waaaay in the back of the engine, up against the firewall. Apparently the theory was that the chain would be so robust, and strong, and dependable, that it would never have to be serviced. You can probably guess what happened next.
Yes, that's right:
it had to be serviced.
You see, as it turns out, the chain itself didn't have any problems with dependability. But Audi, being Audi, decided to use substandard materials for the chain tensioners, and the cam adjusters, which are two related – and highly important – components that keep the chain turning around and around and around every time you drive the car. The result is that these parts eventually fail, requiring the replacement of virtually everything you see in this amazing image of an Audi S4 engine worryingly sitting outside an Audi S4:
View attachment 363367
Apparently, what happens is this: you're cruising along one day in your 2004-2009 S4, listening to electronic dance music, thinking about how cool it would be to stance a Rolls-Royce Phantom. And all of a sudden, you hear a little rattle coming from the engine. This is the sound of your timing belt wobbling around like a toddler in a McDonald's ball pit.
Now, I know what you're thinking:
this doesn't seem so bad! Hoist the engine out of the car, replace a few tensioners, and a few adjusters, and maybe a timing chain or two. And then you're good for another eight years!
Well, here's the thing: there's no such thing as "not so bad" in the world of used Audi repairs. According to
this excellent summary of the problem over on the Audi forums, an Audi dealer charges around
eight grand to fix this issue. You want to do it yourself? No problem. The
parts alone are three grand, and then you have to consider the hours you'll spend under the car, covered in grease, wondering why the hell Audi designed this vehicle so that it could only be fixed by a creature the size of a cicada. All for a car that's only worth about fifteen grand, according to average pricing on AutoTrader.com.
Now, since this column will undoubtedly hit the Audi forums – a group of folks who haven't exactly been my biggest fans, ever since
I once said that "a vehicle made entirely by chimpanzees using random car parts" would be more reliable than an Allroad – I should issue a disclaimer. This issue
might not affect all V8 S4s. Some people have made it to 150,000 miles without issue. Some people have suffered the failure at 75,000 miles. But in the world of $8,000 automotive repairs, "might not" is hardly a comfort – especially since the problem could present itself at any time, without warning. Just a little rattle, coming from the engine. And that's when you know you're not buying name brand toothpaste for the rest of the year."
http://jalopnik.com/this-is-what-happens-when-you-dont-drive-your-v10-audi-1691976274
"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.
View attachment 363368
View attachment 363369
Here's the view into the engine itself.
View attachment 363370
And here's even a look at the back of a valve.
View attachment 363371
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?"
