If the Internet has helped make us car enthusiasts better informed of anything, it's hearing from owners of cars that interest us and learning from them all the little things that go wrong with a car over the course of ownership. This helps us know what to look for when we shop for a car in any category, what the maintenance requirements are, and which models to just flat-out avoid.
This list will cover 10 used cars to absolutely avoid, lest you consider yourself an expert mechanic for that particular model or you really love hanging out at your local mechanics' shop.
Some of these cars are otherwise great but plagued by a catastrophic failure point while others will be death by a thousand cuts, incessantly throwing up little issues until you've spent all your money and patience trying to keep them on the road.
Next time you're shopping used cars, avoid these 10 models.
10 Audi C5 A6/Allroad
The C5-generation Audi A6 (1997-2004), particularly in Allroad form, has an almost comically bad reputation. For starters, any work that needs to be done the engine, including replacing blown turbos (a common issue on the 2.7l V6) and replacing the timing belt every 100,000 miles, requires the removal of the entire front of the car.
"Tiptronic" automatic-equipped cars have a 100% transmission failure rate, requiring an expensive rebuild or replacement. Add fragile air suspension and dicey electronics to the mix, and the Allroad is a wagon that's not worth the fight it puts up.
9 2007 Mercedes-Benz S550
Not all used S550s of this generation are to be avoided, but the 2007 model year has a fatal flaw. In an article for Jalopnik, Tyler Hoover, a man with some experience owning dicey German luxury cars, explains that the 2007 model year of the S550 is the one year to avoid due to an issue it has with one of the V8 engine's timing chain gears. It was made of poor quality materials and tends to fail without warning, and it can do terminal damage to the engine. The repair requires an engine-out teardown, if the engine can even be salvaged. The solution? Buy a 2008 or newer model, as they don't have the same flaw.
8 Any 1990s Cadillac With A Northstar V8
Old GM vehicles generally make great used car bargains. Most of them are reliable, cheap to repair, comfortable and practical (if a little boring). But GM is not without its faults and neither was Cadillac's early-90s flagship aluminum block, 4.6l, 32-valve V8 it called "Northstar."
The unit was used in tons of cars through the decade, including the 1993 Allante, the STS, the Deville, and the El Dorado. The engine's flaw has to do with the cylinder head bolts backing themselves out of the softer aluminum engine block, causing blown head gaskets, oil leaks and other issues that can lead to serious and irreparable damage to the block.
7 Volkswagen Touareg V10 TDI
Needless complexity and difficulty of repair plague most used German cars but few more so than the first-generation VW Touareg SUVs fitted with the TDI V10 diesel engine, sold from 2004 to 2006. It was an extremely complex powertrain, certainly more complicated than gasoline-powered Touaregs. It has electronic air suspension and complex ECUs to run everything, both of which tend to fail. It's also known for devouring its turbos, for interior electronics to fail and other build quality concerns with VWs of the era.
6 BMW E65 7-Series
Please excuse me a second reference to Tyler Hoover, but he has also exposed all the issues you will encounter if you, as he did, buy yourself a used E65 generation BMW 7-Series. These were the first of the Chris Bangle-era of BMW styling in the early-2000s, but its odd looks aren't what should put you off. These cars leak all of their vital fluids from every conceivable point, they have timing chain runner and injector problems with their V8 and V12 engines, air suspension failures and finnicky interior electronics.
5 2003-2007 Maserati Quattroporte
Few European luxury cars can match the troublesome behaviour of the pre-2007 Maserati Quattroporte. This car's engine and gearbox were both derived from Ferrari, and were thus both extremely demanding on maintenance. However, it's the gearbox that really seals the car's fate.
Pre-2007, Maserati used an electronically-controlled robotized manual gearbox, based on Ferrari's "F1" paddle-shift gearbox design. Like all Ferraris fitted with the system, it gave the QP diabolically bad shift performance at ordinary speeds and it would devour its clutches at a such a rate that this comfortable and rather handsome sedan became virtually un-drivable.
4 2000s Nissan Models With XTRONIC CVT Transmissions
You'd think that a mid-2000s Japanese economy car would be a fairly safe bet for a cheap, reliable daily driver. Most of the time, you'd be right, unless the car in question is any Nissan from 2007 to 2014 with the XTRONIC CVT transmission. Not only are they soul-sucking to drive on a good day, but they are also notorious for complete and catastrophic failure around 100,000 miles. The problems were so widespread across the brand's model range that it is still caught up in recalls and legal disputes.
3 Dodge Caliber / Dodge Avenger / Chrysler 200
RELATED: The 15 Most Unreliable Cars Chrysler Has Ever Made
2 Mazda RX-8
Let me preface this by saying that the RX-8 is a phenomenal sports car and, if you can find one that was owned by someone who maintained it properly, and you're prepared to commit to this car's needs, it will reward you beautifully.
But therein lies the problem with the RX-8: it's very needy, and if you are not vigilantly keeping on top of everything you have to do to maintain a rotary engine, you're going to become yet another engine-out rebuild story, and the money you saved buying a cheap RX-8 over something like a 370Z or an FR-S/BRZ will be eaten up by repair bills.
1 BMW E60 M5
Every masterpiece needs a character flaw, and in the case of this otherwise sublime BMW, its engine hides its dark, third-act reveal secret. The 5.0l S85 V10 engine has notorious issues with its rod bearings, which can fail at any moment and grenade the engine from the inside.
It also has issues with throttle actuators, oil pumps, and particularly with the SMG robotized paddle-shift transmission. Most M5s were sold with this kludgy gearbox, although BMW did offer this car with an optional 6-speed manual. Those are incredibly rare, and the rest of the SMG-equipped M5s are vast money pits not worth diving into.