Yuille36

I can tell you that head bolt failures are real, but it's a very percentage compared to the amount of M156 engines produced. No one can predict when it will or will not happen. It's a crap shoot.
So, you can either pay now, which is cheap insurance knowing that you will not experience any future failures, or you can pay later which can be costly, if you blow a head gasket, or have a catastrophic engine damage.
I will say this, if your planning on keeping your vehicle for many years to come, I would pull the trigger and have it done. It's cheap insurance. If not, then just remember that there are thousands of M156 engine out there without the newly revised head bolts.

CQHall

The only thing you can tell about me is that I'm looking for numbers, not anecdotal, "this one guy on the forum back in 2010 had it happen to his GF's dad's car...", "evidence".

I work with numbers for a living and I trust those.

I never said it doesn't happen. I'm looking for failure rates.

CQHall

Regarding numbers, here's an example:

Audi currently has an issue with their 4.0L TT motors that are used in several cars (A8, S8, S6, S7, etc...). It has a design flaw where there is a screen that's designed to keep large particles in the oil from getting into the turbos as they are being lubricated. The problem is that the screen is too small and it simply gets gummed up and eventually starves the turbos of oil causing them to fail causing a $10K repair. The screen is about the size of a nickel but it's deeeeep inside of the engine. Audi was aware of this as they had several revisions of that part and a service bulletin. But, no recall (of course).

TSB: https://static.nhtsa.gov/odi/tsbs/20...53123-9999.pdf

Forum chatter:
https://www.audizine.com/forum/showt...own-Turbo-Poll

NTHSA response: https://static.nhtsa.gov/odi/inv/202...009-83219P.pdf

And....Recall: https://www.autoevolution.com/news/a...er-185179.html

That's what I mean by wanting numbers.

HLG600

You're attempting to dismiss the real world experiences of many on a subject matter that was already put to rest by MB-AMG a long time ago.

Unfortunately, failure rates were not formally tracked on this issue. Even if Mercedes issued a recall, it would be for everything manufactured before the correction was implemented ~2011.

In any case, what value is there in any predictive modeling on the likelihood of a component that is known to be defective (and superseded as a direct result of that defect) to fail?

If you take a step back and understand the nature of why the original head bolts fail, you'll understand that all engines with the defective ones have a very high risk of failing well-before the usable life of the engine is exhausted.

Okay. The recall refers to impacted range, not failure rate.

https://mbworld.org/forums/c63-amg-w...y-2011s-2.html

Applying your example to the head bolt issue, any M156 with an engine serial number below 156983 60 060658 is using the original head bolts that have two defects (one design and one manufacturing) and are at risk. If you really want to know the volume of engines built in this range, you can look up and aggregate production numbers of M156-cars from 2007 to early-2011.

CQHall

1: Quote where I dismissed someone's personal experience with this issue.
2: The failure rate (albeit a sample of forum users) is in the poll linked above.
3: You are operating under the assumption that I don't know why the head bolts fail. Hell, I can draw the diagram of the problem.
4: Yes. My car engine's serial number is so early that it's in the affected range. I've been aware of that since I got the car. And I assumed as much when I bought a 2008.

So, my opinion is, indeed, informed.

HLG600

1. How about labeling discussion on the subject here as conjecture and challenging people's documented experiences as "evidence"?
2. That's technically not a failure rate...but if it helps, all the better.
3. Cool, draw it. If you truly understand why then you wouldn't need the NHTSA to confirm the matter for you.
4. Good that you're aware. How many miles when you bought it vs. now? If you're not the original owner, ever check if they were replaced already?

Your opinion is incomplete, due to fixating on the numbers "because you trust them" and not factoring in the context.

I repeat my earlier question: What value is there in any predictive modeling on the likelihood of a component that is known to be defective (and superseded as a direct result of that defect) to fail?

CQHall

I'm out.

OP. Good luck with your decision.

SleepersRock

Yup. Best sounding car, especially with resonators removed. I get complements all the time.

That said OP:
Be prepared to drop 5K for the suspension if that's not done already. Oil leak is probably valve cover gaskets. That's the only leak I ever had.
Replaced headbolts while I was in there too for peace of mind, but the originals looked fine.
Drive Belt failed at exactly 100K.
I've bent 3 aftermarket 19in rims so far.

Other than that it mostly been maintenance from when I bought it at 58k to where it is now at 120K.
I'm going to end up driving this thing into the ground. Can't imagine selling it.


The car is expensive AF to maintain but I'm still constantly getting people giving me a thumbs up or rolling down window to give me complement. Its worth even more to me now as I can write off most of my repair costs, but it was worth it even when I couldn't as W2 worker.