Caveat Emptor is something the Romans never imagined would apply to purchasing motorized horseless chariots, but the famous Latin phrase meaning “buyer beware” should be at the forefront of everyone’s mind when shopping for a used car.

Despite my pretentiousness of opening this column with a Latin lesson, I can tell you I’m not a smart man. But I do have a very particular set of skills. Skills I have acquired over a very long career of asking, “What will it take for you to buy this beautiful 1997 Chevy Malibu today?”

That’s right. I was a used car dealer. After a decade in the car business, I semi-retired with a few pieces of my soul still intact. I am left with the superpower of coaxing people into buying polished turds, as well as an encyclopedic knowledge of which used cars to avoid.

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Before, I used this great power with great irresponsibility. Now I will use this power for good, keeping you from buying a disaster on wheels.

This brings me to my first official PSA, short for Pile of Shit Announcement. Thanks to Jalopnik, everyone knows the engineers at BMW enjoy making engines that function like hand grenades and that owning an Audi Allroad will leave you so broke you consider it a win if you can trade it on Craigslist for a Sega Dreamcast.

What many people don’t realize is no automaker is immune to making critical mistakes in engineering. Even venerable brands like Honda and Toyota have horrific examples of “what the fuck were they thinking?” that run counter to their normal levels of dependability.

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Certainly Mercedes-Benz, a company touted as “engineered like no other car in the world”, have engineered out of this world mistakes. Which is why today’s PSA states: For the love of God, don’t buy a 2007 Mercedes S550.

2007 was the first model year this all-new S-Class went on sale in the U.S. It was meant to re-establish Mercedes’ dominance in luxury land yachts. With sexy wheel arches, unparalleled ride quality, and an endless array of gadgetry like four different seat massage settings, affluent buyers were lining up to pay close to six figures for the new S.

Fast and Vigorous, please.

Nearly a decade later, nice examples can be picked up for a piddly $15,000-$20,000. It seems like a screaming deal. But I am going to tell you that even if the salesman puts a gun to your head, don’t ever buy one.

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Many of you are probably thinking I’m going to dive into several of the well known problems that plagued Mercedes-Benzes of this era. Things like the air ride suspension or the vast array of electronics, both of which fail in spectacular ways. You’re wrong.

With a good independent mechanic, or if you’re handy with a screwdriver and swear words, you can keep these systems going reasonably well. What brings this car to its knees is a small part you would never think of.

Friend, let me introduce you to this little gear. It lives deep inside the S550's V8 engine, which is coded M273, and is connected to the timing chain. Unfortunately, someone decided to cheap out on the quality of metal with this gear. Like someone addicted to meth, the teeth on the gear can start to decay and fall out, with catastrophic results.

The first warning of impending death is a check engine light throwing camshaft timing codes. If, like most careless third- or fourth-hand owners, you ignore this warning light, you’ll notice an increasingly out of balance engine. It will start to gyrate, like Shakira in “Hips Don’t Lie.”

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If you are insane enough to keep driving as the sprocket continues to degrade and the jiggling becomes more intensified, like Beyoncé in “Single Ladies”, the timing chain could eventually slip.

Piston will mash valve, and your car will be dead. Remember the Mercedes in Michael Clayton? That is exactly what happened to him. Exactly.

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With the cost of a used engine around $5000 and installation labor around $1500, for a bit more you could have leased a new Mercedes C-Class.

Let’s say you’re a more fastidious owner, and decide to replace the gear before your engine starts dancing seductively. It’s only a cheap little gear, right? Well this handy video from will tell you exactly how to do it in a few simple, easy steps.

  • Step 1: Remove the engine from your car.
  • Step 2: Remove the front cam covers, secondary air pump, guide pulley, thermostat housing, belt tensioner, oil filter case, vibration dampener, water pump, coils, valve covers, timing chain adjuster, and timing cover.
  • Step 3: Replace the gear.
  • Step 4: Somehow remember how all of this goes back together, then do that.

It’s that simple!

If this job seems a bit too challenging, you can farm it out to your local Mercedes dealer. They certainly have a lot of practice at these, and are happy to bill you the bazillion labor hours it takes to get it done.

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Sadly, the issue was not contained only to this year and model. I chose the 2007 S550 as the flagship example. Virtually the entire Mercedes model lineup (non-AMG, that is) with a certain serial number range of V6 and V8 gasoline engines during the 2006 and 2007 model years were affected.

The V6 engines, called M272, have similar defective gears in their balance shafts. Like the V8s, they can wear out prematurely and cause the same kind of death-jiggle.

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With the cost of parts and dealer labor rates, you’re still probably not far off from the cost of putting in a used motor. With some lesser models, like a 2006 C-Class, the repair would exceed the value of the car.

The odds of this failure happening to you are probably about the same as losing a game Russian Roulette with a single bullet in the chamber. Not as huge as they could be, but would you want to take that chance?

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The only practical solution? Buy a 2008 S550, making sure the engine serial number is not in the affected range. Mercedes fixed their mistake by then with stronger gear teeth, settled a class action lawsuit regarding the matter, and moved on to make other mistakes, like the CLA-Class.

This has been a PSA brought to you by Hoovie at Jalopnik.

Correction: I originally stated the 2007 S550 V8 engine had a balance shaft which the faulty gear was attached to. Only the V6 cars have balance shafts, but both engines have a similar gear attached to the timing chain with inferior metal quality. This post has been updated to note that difference, but the overall point stands—buy a 2008 or later S-Class. I apologize for the error!

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Tyler “Hoovie” Hoover went broke after 10 years in the car business and is now selling hamburgers to support his personal fleet of unreliable European cars. He documents his exploits on Twitter @hooviesgarage and will soon be writing for Drivetribe.