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Possibly the most critical factor in car ownership is its reliability. Everyone pays for a vehicle once, but those who don’t do their research or choose with their heart can subject themselves to a lifetime of financial and emotional pain. Now, whatever constitutes something as “worth it” is entirely subjective; however, I’d argue that more than a few models toe that line so well that we could all see ourselves sitting behind the wheel. Enthusiasts count them out as unreliable, and that is just about a fact, but their positive qualities shine so brightly or uniquely that ownership almost makes sense. In case you haven’t heard of them or are looking to make a potentially financially ruinous decision, here are some of the coolest unreliable models ever produced. 

Mercedes-Benz C36 AMG

AMG wasn’t always part of Mercedes. In fact, they started as a standalone tuning and racing company like Alpina. Eventually, after decades of collaboration and success, Daimler-Benz acquired a majority stake in AMG and made them a subsidiary. Their first official model together as Mercedes-AMG was the W202 C36 AMG. It was meant to continue the fight against the BMW M3 and was a fierce competitor, although the lack of manual transmission certainly hurt it. It was a different take on a family sport sedan and provided plenty of competition on paper, but it did suffer from a few issues. To be fair to the C36, it isn’t the most unreliable Mercedes out there, but the severity and frequency of its largest issue meant nearly every one of them was crippled.

1993 mercedes-benz c36 amg

The C36 AMG looks like a fantastic but forgotten model on paper. Mercedes offered it between 1994 and 1997 and built it upon the first C-class platform, the W202. In typical AMG fashion, an aggressive exterior treatment featuring unique bumpers and side skirts separate the C36 from its non-AMG siblings. It rode on AMG’s classic monoblock wheels and featured stiffer and lower dampers all around. The engine was the hand-built M104.941, a naturally-aspirated 3.6-liter inline-6 that produced about 270 horsepower and 280 lb-ft of torque. Unfortunately, it was only offered with a four or five-speed automatic, depending on the model year. Sport seats covered in black leather and surrounded by walnut trim adorned the luxury interior. The C36 was precisely what you’d expect from an AMG car today in a perfect representation of that era. 

Not everything that went into building the C36 AMG was good, though. Dieter Zetsche, a head engineer at Mercedes-Benz in the early nineties, chose to use an eco-friendly, biodegradable wiring harness sheathing. No matter the model, its condition, or how it was driven could’ve saved them from the nightmare that awaited it. A few years after their production, owners began getting reports of crumbling wiring harnesses. The eco-sheathing Mercedes chose to use cracked and disintegrated over time, leaving wires exposed in the engine bay. Even now, a Mercs of that era can be found with exposed copper under crumbling sheathing and insulation. The exposed wires all intermingling were occasionally enough to take out computer systems and other electrical components connected to the engine harness. Replacement harnesses carried four-figure price tags, not to mention the cost of a new ECU or HFM, and owners were left with no choice but to replace them to keep driving. 

The C36 AMG had more issues, too. The M104 did chronically pop head gaskets, but that gave owners the excuse they needed to fix the likely-leaking timing cover. Other more minor issues included leaking differential seals, easily worn suspension bushings, tons of brittle engine bay components, and shrinking interior panels. Thankfully, the C36’s problems are primarily fixable. Replacement harnesses can be tough to find and are still reasonably costly but are made from modern materials. The head gasket is AMG-specific (HWA 104 016 01 20) and is more expensive than any other M104 gasket, but it’s readily available, as are the rest of the components needed for that job. The other odds and ends can be found new or across the many forums dedicated to Mercedes. The C36 AMG wasn’t Mercedes-AMG’s best or most reliable model, but it represents the beginning of a legendary partnership. If you can find one with all of the significant servicing completed, I don’t know why you wouldn’t go for one. 


BMW E60 M5 & E63 M6

The E60 M5 and E63/64 M6 are some of the most famous M cars to leave Munich. They were filled with Formula 1 derived technology and modern luxury comforts, making them one of the best sports sedans/coupes of the time—or at least they should’ve been. Chronic issues with components small and large plagued every owner regardless of treatment. These two are part of BMW M’s most celebrated era, yet they regularly leave their owners for dead and without any money. 

BMW M6 E63

The defining characteristic of the E60 M cars is the engine. BMW was well into their partnership with the Sauber Formula 1 team and manufactured the V10 engine used in that series. In linking their F1 prowess with their streetcars, BMW built the S85 for the M5 and M6. The S85 is a 5.0-liter, naturally aspirated V10 that pushes out 500 horsepower and revs to 8250 rpm. It was the jewel of the M division, and journalists ranted and raved at its sound and power upon testing. 

It even won many awards, including the 2005-2007 Best Performance Engine and the 2005 and 2006 International Engine Of The Year. It was the darling of the motoring world and only got better with the car built around it. 

BMW M5 M6 S65 Engine V10

The rest of the M5 was generally viewed as sublime. The classic M division characteristics were present, as were a handful of new options designed for more adjustability. The SMG-III transmission had six shift settings, the M-Variable rear differential had three settings, and the suspension had two. It was to be the best one yet, an instant future classic. Fifteen years later, the S85 M cars are arguably classics, but not all for the best reasons. The snarling V10 quickly became a time bomb, with the early cars suffering from some catastrophic issues. 

Both the S85 V10 and the S65 V8 were bitten by their connecting rod bearings being too weak. Owners regularly spun the bearings and sent metal bits throughout the oiling system. In a best-case scenario, the engine was ok and the rod bearings could be replaced to the tune of over $10,000 at the dealership. Worst case scenario, a new engine was required. In both cases the front subframe and suspension required removal. 

Alongside the bearings were the VANOS pumps and high-pressure feed lines failing regularly. Both VANOS-related problems are easier to fix than bad rod bearings but are still very labor and money intensive. Other smaller bits like VANOS solenoids, throttle actuators, and thermostats became the cheaper common failures. That’s relative, though, as the actuators are over $650 apiece, and there are two of them.   


So a temperamental engine in an otherwise solid package? Not quite. The SMG-III transmission fitted to the vast majority of M5s and M6s was about as fault-free as the engine. It was a technologically advanced transmission for the day but was ultimately a flawed system, hence the switch to the dual-clutch gearboxes. The SMG’s complex hydraulics systems let it down everywhere with pump failures, pump motor failures from debris, and pump accumulator failures affecting nearly every gearbox. Then there were the mechanical and electronic failures from the clutch release bearings, PLCD sensor, and the poorly heat-shielded wiring. None of the components are inexpensive, and a majority of the fixes necessitate opening the gearbox. 

There’s more than that, too, with things like valve cover gasket and differential seal gaskets leaking and the odd worn suspension bushing, but I’m sure you get the point. Do all of them suffer from these issues? No, they don’t. The problems they have don’t carry a guaranteed failure rate even though they’re pretty standard. Look around, and you’ll find plenty of owners who are proud to be breaking the stigma of the E60’s unreliability. There’s also a healthy aftermarket scene and plenty of informative forums that offer improved parts and years of insight on how to repair and maintain the finicky models. Like any performance car, the S85-equipped M cars are a risk, albeit a debt-inducing one, so proceed with great caution when ownership thoughts begin to creep in. 


Audi Allroad C5

Subaru had an absolute smash hit when their lifted Legacy Outback debuted for the 1996 model year. As another company whose cars almost exclusively used all-wheel-drive and whose race teams had years of rally success, Audi saw their sales take an unexpected hit from the small Japanese company. Not to be outdone by their “own” formula, Audi released the Allroad. The lifted wagon was a more refined and upscale Outback fighter with a then-cutting-edge suspension system, transmission, and engine. The allroad was a success, but owners out of warranty were hit with a load of expensive and unexpected repairs that have now become synonymous with this generation of Audi.


On paper, the C5 allroad was a dream come true for enthusiasts. Under the hood of a majority of the Allroads was Audi’s twin-turbocharged 2.7-liter V6. Sharing many components with the S4, it produced a healthy 247 horsepower. If it wasn’t the turbo V6, it was a 4.2-liter V8. Backing them up was a five-speed Tiptronic automatic or a six-speed manual that put all the power down through Quattro all-wheel-drive. Adding the “all” to allroad was the factory air suspension capable of raising itself to over eight inches of ground clearance. Audi then wrapped all of that technology up in their C5 A6 Avant chassis, a relatively handsome wagon body clad with plastic wheel arches and bumpers for that offroad protection. The Subaru Outback was put on notice; the Germans had arrived. 

The wagon was well received and sold well, but owners were hit with more than a few gremlins as their cars aged, and those issues haven’t gotten any better. The twin-turbocharged V6 was fairly potent out of the box and is well known now as a decent-performing engine. They made good power and were receptive to performance-enhancing modifications. Unfortunately, several issues became infamous as their mileage increased. The turbochargers developed into a widespread failure point, and because of the engine’s tight packaging, replacing the turbochargers typically requires engine removal. However, while that may sound like a nuisance, and it is, engine removal does make it easier to fix some of the other common faults.

Front and rear crankshaft seals, valve cover gaskets and spark plug tube seals, camshaft seals and plugs, and camshaft chain tensioner seals are all regular leak points on the 2.7T. On top of that, timing belt and water pump services need to be done on time, and a majority of the plastic PCV and emissions bits will likely be very brittle if not replaced already. The 4.2-liter V8 wasn’t much better. Oil leaks were less common, but they developed timing chain issues that required a complete engine removal.

Backing up those temperamental engines was either a six-speed manual or a five-speed “Tiptronic” automatic. The manual transmissions are stout and do well in modified applications, but the Tiptronic automatics don’t. Tiptronic issues are rife within that era of Audi products with slipping, hard shifting, and general hesitation all plaguing the slushboxes. Manual swap kits are available and make sense for anyone dead set on owning one of these. 

The other swap kits available for the allroad are for the suspension. The advanced air suspension fitted to the allroad was great when it worked, but many owners have found that to be far less frequent than expected. Just about everything that could go wrong with them, did. Torn air springs were normal but not always enough to prevent inflation, so it would leave the compressor constantly running to keep the bag inflated, eventually killing it. Valve blocks can leak or get sticky, causing half of the suspension to deflate while parked, and if that wasn’t enough, the various airlines and sensors could also cause issues. Many current owners find themselves looking at a coil-spring and damper setup in place of the heinously expensive factory air suspension. 

The allroad had all of the right parts and specifications to be a really great wagon, but its reliability let it down. These days, you can find them pretty inexpensively, thanks to their known reliability issues. That unreliability doesn’t have to be its downfall, though, as we sell quite a few parts that rid the air suspension and engine of their faults. The Arnott air springs and shocks are a common replacement in the allroad community, and for a good reason. Their springs use the OE Continental bladders while coming in at around a third the cost of a Genuine unit. We also offer Arnott’s compressors which are made by WABCO, the Audi OE supplier, at under half of the cost of a Genuine Audi piece. Oil seal kits and turbocharger upgrade kits are out there for allroad, too. If you’re still interested in an allroad after all of that, then find one with as much service history as possible. Previous work doesn’t guarantee reliability but should make ownership easier on the wallet. 


Volkswagen Passat W8

Volkswagens have always been for the masses, and even though their name is the literal example of that, that didn’t stop them from attempting to change. In the early ’00s, VW introduced two new models to their lineup in a move projected to boost sales in segments never before filled with a Volkswagen. At the top of the range was the Phaeton, a full-sized sedan sharing the seats, suspension, and W12 engine with the Bentley Continental, albeit sans turbochargers. The other was a then-four-year-old Passat featuring the new W8 engine. The unique engine in an established chassis could’ve been a hit, but it was hit with some recalls along the way to becoming infamously unreliable in the VW community.

2001 Volkswagen Passat W8 B5.5

The Passat’s party piece was the W8 engine. VW had never put an eight-cylinder in one of their cars before but dove straight into the deep end when they did. The W8 is made up of two banks of narrow-angle V-engines joined at the crankshaft, allowing it to be shorter in length than a traditional V8 and fit under the hood of the Passat. With 270 horsepower and 273 lb-ft of torque, the 4.0-liter W8 was no slouch and could push the big sedan to 60 mph nearly as quickly as the Mustang GT of the day. Back in 2002, a buyer could option their W8 sedan or wagon with a six-speed manual, too, which sent its power down through VW’s 4Motion all-wheel-drive system. On paper, it’s the perfect daily-driver recipe for any automotive enthusiast out there, so it’s a shame it developed so many issues. 

The W8, while exciting and new, had more than a handful of issues that have since plagued nearly every owner—chiefly among which is the failure rate and severity of its camshaft adjuster solenoids. Fitted before them in their oil passages are small screens designed to keep debris out. But instead, they break up over time and become that very debris. All of that metal clogs oil passages and hurts bearings, often ending up with extensive service requirements if not an entirely new engine. That’s not a massive issue for common engines, but the W8 was so expensive and high-tech when new that it was troublesome finding parts for it, let alone a specialist who had experience servicing them. But hey, on the bright side, the engine, subframe, and transmission removal required for cam adjuster work allowed Tiptronic-automatic-equipped W8 owners to replace their torque converter, another almost guaranteed failure. 

2001 Volkswagen Passat W8 Wagon B5.5

With the significant bits out of the way, there are still many minor issues not exclusive to the W8 but rather the entire B5/5.5 lineup. As someone who’s run out of gas more than once thanks to faulty fuel level readings, the health of your fuel level sender is critical; a shame then that the W8 and other 4Motion VWs have frequent failures. If the senders aren’t causing fuel issues, it is a bad fuel pump control module. Those sit at the bottom of the spare tire well where water is known to collect, frying the W8-exclusive module. Do you want to be warm while you drive your all-wheel-drive VW in the cold? Go for it, but don’t put the seat heaters on too high, or they’ll burn a hole through the seat. On top of that are the faulty brake light switches that prevent you from shifting out of park and frequent CV boot rips.

But don’t take that as a reason not to buy the car, as it’s more of just a warning because the W8 Passat is unique in terms of Volkswagen and powertrain. The W8 never saw action anywhere else but made plenty of power and a heavenly noise when used. The B5 chassis it was wrapped in has aged beautifully, featuring understated but handsome lines, standard bi-xenon headlights, and exclusive wheels. As the top-range Passat, VW clad the interior in Nappa leather with wood and chrome trim everywhere. For the money, which is well under $10,000, in case you were wondering, nothing will come close to its uniqueness and cool factor. However, you’ll be paying the price. 


Volkswagen Phaeton W12

VW was swinging for the fences in the early 2000s, thanks to Ferdinand Piech with the Passat W8 and Phaeton W12. Their upscale, upmarket push would be championed by an all-new model developed in tandem with the Bentley Continental and Flying Spur, sharing their components. It was as big as a Mercedes S-class and was meant to rival them, too. But a lack of marketing and poor judgment of its segment meant the Phaeton never sold anywhere near what Volkswagen hoped for. However, that’s probably a good thing, as the Phaetons became synonymous with expensive and constant problems.

Volkswagen Phaeton W12

The W12’s development spanned over ten years by the time it entered service in a production vehicle. It first appeared in an Audi concept before finding itself in the VW Syncro, Roadster, and Nardo concepts between 1997 and 2001. Two examples of that final concept were modified for 24-hour endurance speed records that were broken on each attempt they made. It was well developed, and the naturally aspirated, 6.0-liter unit that sat in the Phaeton was a strong performer. With between 420 and 444 horsepower on tap depending on the model year, the Phaeton could at least keep up with its more established rivals in a straight line. The standard all-wheel-drive system ensured the flagship was capable in poor weather conditions, too. All good features in a car no one was looking for.

It only got exponentially fancier inside the cabin. Hidden vents, a four-zone climate control system kept each occupant comfortable, but so did the heated, cooled, and massaging front and rear seats it shared with Bentley. Touch surfaces were leather, wood, or the nicest plastics that VW had to offer. Each window had its own defogger vent, and the rear seats received automatically retracting power headrests. Typically manual adjustments like seat belt height and vent flow used electronic controls instead. Even the glass was upscale—the side windows were all double-pane insulated to keep out road noise. All of that interior comfort was capped off by the air suspension taken from the Bentleys.  

Volkswagen Phaeton W12 Rear Seats

The near six-figure price tag and Volkswagen badge were enough to keep buyers away from the Phaeton when new, and the subsequent repair costs and time spent in dealer service centers has kept away second-hand ones. The Phaeton’s technologically advanced systems and incredible luxury looked great on paper, but owners quickly learned that they weren’t always the easiest to live with. Its complex electrical system used more than a handful of different computers to monitor every part of the car. If they didn’t all see eye to eye, codes would be thrown, rough running was possible, and the vehicle might not have started. Transmission issues became fairly commonplace, too, with slipping in one of the first three gears being the main complication. I know that doesn’t sound like much, but the faults were only half of the problem.

Each Volkswagen dealership was required to have a Phaeton-trained technician, though that didn’t help in many cases. The kinds of issues many Phaeton owners dealt with regularly had dealerships in touch with the VW factory for assistance. Cars would be stuck in service for weeks at a time while technicians and VW threw parts at them in hopes of a cure. Making matters worse was that parts were tough to come by in the states. That parts availability hasn’t gotten any better, so repairs are still several weeks long and likely several thousand dollars. Things like A/C vent motors, window regulators, massaging seat motors, and sunroof motors are regular sticking points for older cars, and their Bentley connections haven’t made them affordable. The most serious Phaeton owners in America these days have multiple parts cars waiting to be pulled apart as failures of modules, motors, and sensors are just that common.

Volkswagen Phaeton W12

Even with the bank account-crushing running costs and general unreliability, they have a cult following. When functioning correctly, they’re as refined as any luxury sedan of the day, if not more so. The W12 is, relatively speaking, one of the most reliable parts of the car, and it isn’t uncommon for them to make it well beyond 100,000 miles with the proper care and maintenance. As a whole, the Phaeton would be incredible value for money if modern and proven electronics could replace the old stuff. Someone get working on that.

Having some time to think about it, these models are reliable, but just not in any beneficial way, and that’s OK! Just because they cause us financial and emotional pain doesn’t mean they shouldn’t be celebrated. Each of the models on this list is unique, whether it's within their own brand or generally. With funky drivetrains and luxurious complexity, they deserve a bit of love. Not too much, though, or you’ll likely find yourself stranded and moneyless. If you have your own horror stories about the vehicles above or another unreliable ride, let us know about it in the comments below! As always, subscribe to our YouTube channel and follow along on the DIY Blog for more daily content.

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Written by :
Christian Schaefer

Car and motorsports-obsessed writer/editor for FCP Euro's DIY Blog. Constantly dreaming of competing behind the wheel or searching for another project. Owner of a turbo Subaru Forester and a ratty Porsche 914, neither of which are running.

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