10 Surprisingly Unreliable Cars

By James Mackintosh, 01 November 2010

There are some cars you buy, expecting a certain degree of mechanical fallibility. In some cars, it's part of the character of owning one.  In others, it's an inherent design issue that's well known and you learn to work around it.  No one really buys an old Alfa Romeo expecting it'll never have wiring issues.  People with a Citroen SM-Maserati didn't purchase it for it's Swiss Watch durability.  Only the truly misinformed expect an old RX-7 to spend more time on the road than making the lawn look pretty.

But some vehicles have an absolutely baffling reputation for reliability in the face of considerable evidence.  These are cars that people buy because their reputation leads them to believe they'll enjoy a few years of trouble-free motoring, and it's an unpleasant surprise when their wallet bleeds itself dry keeping them on the road.  Here are a few to keep an eye out for that you might not have been aware of.

BMW N54-powered vehicles

This was the original idea behind this post.  For those not well-versed in BMW-ese, the N54 is BMW's 3.0L iron-block straight six, fitted with twin sequential turbochargers that is fitted to almost all of BMW"s range in various states of tune, including the 1, 3, 5, and 7 series, as well as the X5, X6, and Z4.  When it came out in 2006 as a replacement for the M54 3.0L engine, the automotive press and consumers alike were ecstatic.  The N54 made a ton of power (306bhp) with almost no discernible turbo lag, a silky straight-six roar, and returned respectable fuel economy.  Finally, the 3-series had the power to not get embarrassed by Infiniti G35's!

Problems arose pretty quickly, though.  It shouldn't have been surprising; the N54 was BMW's first gas-turbo engine since the 745i in the mid-eighties with it's 3.2L M102 straight six.  The issues weren't really related to the turbochargers themselves, so much as the direct injection system and it's high pressure fuel pump (HPFP) that supplies the ridiculously high fuel pressure needed to run the injection system.  No one really knows what exactly causes the high frequency of failures with the HPFP, but some third parties suggest it's related to the low-pressure fuel sensor.  Regardless, since the motor came out in 2006 the fuel pump has been through 6 different designs in the last four years, and owners on BMW boards are still reporting pump failures after only a few thousand miles.

After a few years of dodging warranty claims and calling it user error or attributing it to regional gasoline quality (a trend we'll see again), BMW issued a voluntary recall that covers 160,000 BMWs powered by the N54 engine.  Considering the failure of the fuel pump can lead to the engine stalling and the loss of power steering and power brakes, it's a legitimate safety concern.  If your twin-turbo BMW is exhibiting symptoms like an unwillingness to crank over in cold weather, stalling or sputtering at idle, or a check engine light and limp-home mode, then your HPFP could be dying.  BMW is now covering this part with a 10-year, 120,000 mile warranty, so that helps.

Mercedes OM603 3.5L Turbodiesels

Mercedes-Benz turbodiesels from the 70's and 80's have rightly earned a reputation for longevity that rivals that of the cockroach.  Old Mercedes diesels are still clattering and sputtering along happily all around the world, from Africa to Oregon, belching fat clouds of black smoke and still accumulating hundreds of thousands of miles.  Chances are, though, that not many of those ancient Mercedes diesels have a 3.5L OM603 straight-six under the hood.

The OM603 was the replacement for the bulletproof OM617 5-cylinder engine found under the hood of the 240D, 300D, 300CD, etc.  There are a lot of nice things to say about the OM603 - it was much less agricultural than the five-cylinder OM617, and it had a very advanced design for the time.  It made more power and torque than the old engine, and got better fuel economy.  The normal 3.0L OM603 was not nearly as problematic as it's bigger 3.5L brother, though.  It did have issues with the diesel particulate filter, which was mounted quite close to the block, becoming clogged and sending soot back into the turbocharger.  The aluminum cylinder heads of early 603's ('86 and '87) were prone to overheating and cracking because of the trap filter as well, although later revisions of the head solved the problem.

The 3.5L engine, found in the bigger 350SD and SDL, had other issues.  Since the bore was increased, the surface area of the head gasket was smaller, and the larger turbocharger caused increased heat and pressure.  The 3.5L was more prone to head gaskets eroding, which would cause a gradual and then rapid oil leak into the number 1 cylinder.  Although it would just burn the oil for a while, as the erosion continued it would leak faster, eventually hydro-locking the cylinder.  Which would then bend or break the connecting rod, and the bent rod would turn the cylinder into more of an oval, and your motor was toast.  Because of the wider bore of the 3.5L, it was not possible to bore the engine out, so a new block was needed at rather tremendous cost.

Motor mounts that went bad were a problem, too - when they were shot, the block would vibrate a lot more, working loose screws that held the windage tray in place.  These would block oil passages, starving the crank bearings of oil, and it would end up throwing a rod.  The failure rate on these engines was so high that Mercedes was voluntarily replacing some of these engines outside of warranty to keep up customer goodwill.  If you've got a hankering for an old Mercedes diesel, make sure it doesn't have one of these.

Honda/Acura V6 Automatics

This isn't so much for one car or engine in particular, but rather almost anything Honda with a big V6 mounted sideways, and an automatic transmission.  In most people's heads, Honda = Reliability.  Still, every manufacturer has their weak spots, and for Honda it's the combination of an automatic hooked up to a big engine in a heavy car.

Cars affected include 3.0 Accords, 3.2L Acura TL's, Acura MDX's, Honda Pilot/Odyssey/Ridgeline (which all use the same powertrain)... you get the picture.  The problem is related to heat buildup and transmission fluid leaks, which cause the transmission to slip and eventually wear out to the point it won't shift, or won't go into gear in the first place.  This usually occurs at relatively high mileage - hey, stuff wears out - but the overall pattern points to avoiding a V6 Honda with high mileage and a slushbox.  Of course, you were going to do that anyway.  Honda's 3.0 V6 and 6-speed manual in the Accord (and it's bigger 3.2L brother in the TL) is such a delicious combo that you weren't considering an automatic in the first place.  Right?

Honda never issued a recall, but they've been a lot better dealing with the customer service end of this issue.  The warranty on automatic trannys in 98-02 Accords, Odysseys, and MDX's was extended to 8 years/80,000 miles, past the normal 3/36k warranty.  They deal with cases on an individual basis, although if you want a hand from Honda, hopefully you have proof of having followed the schedule maintenance and only used Honda ATF-Z1 transmission fluid.

Toyota 3.0L V6

Sludge.  Yikes.  This issue was half design flaw and half consumer error, but it still should've been avoided.  Oil sludge is what happens when oil gets overused and overheated, and it starts to gel up and leave deposits in oil passages.  Sludge can block these crucial oil passages, leading to bearing oil starvation and engine failure.  Unfortunately, fitting with the Toyota owner stereotype of "where's the hood latch?", Toyota reported many instances of vehicles coming off lease at 40,000 miles with sludge issues... and the original oil filter still screwed onto the block.  Hey, 40,000 miles without an oil and filter change will kill even the best of engines.

However, the issue is also a bit of a design flaw on Toyota's part, although they're reticent to admit it.  The issue centers around the PCV (positive crankcase ventilation) system.  If the car is only driven short distances, the oil never gets fully up to operating temperature, leaving a lot of moisture in the oil.  Over time, this becomes oil sludge, which will block the PCV valves, forcing crankcase gas through the intake.  Eventually, sludge will clog the oil pickup in the crankcase, starving the engine of oil flow and killing it.  The Toyota 1MZ-FE (3.0L) and 3MZ-FE (3.3L) used in cars like the Camry, Solara, Sienna, RX300/330, ES300/330 are the most frequently affected.  Bottom line?  If you want to avoid the "sludge monster", change your oil and filter every 3,000 miles.  Don't do repeated 1 mile trips that never allow the engine to get to operating temperature.  Don't be a typical Toyota owner, and a Toyota V6 will last you for years.

BMW M60 V8

Another BMW engine snafu.  The M60 was BMW's first modern V8 engine, which replaced the M30 "big six" in the 5 and 7 series lines.  It was quite a high-tech design for the time: aluminum block, aluminum chain-driven twin-cam 4-valve heads, forged crankshaft, magnesium valve covers, direct ignition, all the works.  Also new for the M60 V8 were Nikasil cylinder liners, which were made of a combination of Nickel, aluminum, and silicon rather than the traditional iron cylinder liners.  This proved to be an issue.

The Nikasil liners suffered significant corrosion when low-quality gas with high sulfur concentration was run through the engine, leading to cylinder liners failing near the top of the piston and allowing for significant compression loss.  Over time, it would literally cause the motor to not start at all.  Since Nikasil was a spray-in liner, it wasn't possible to simply bore the block and sleeve it with iron liners, so the only solution was to replace it with a short block using the later Alusil lining, which didn't suffer from the corrosion issues that Nikasil did.  Although the only regions that really suffered from this issue were America and Brazil, it still did not reflect well on BMW, who extended a 6-year 100,000 mile warranty to engines made with Nikasil liners.

VW/Audi 1.8T, longitudinal mount

For some reason, the transversely mounted 1.8T (In the GTI, Jetta, TT, A3, etc) doesn't suffer nearly as many problems on the whole as the longitudinally mounted 1.8T in the (B5, B5.5) Passat and (B5, B6) Audi A4.  One failure all 1.8T's seem to have in common, though, are the coil packs.  Early-build 1.8T's (like the big-valve motor in the first A4's) used Hitachi-branded coil packs that literally bolted to the cylinder head.  These almost never fail.  Later 1.8T motors switched to Bosch sourced coil packs, and these have an unusually high failure rate, which will lead to misfiring, stuttering, and the dreaded "limp home" mode.  Sometimes they just get pushed off the plug by vibration (of if you're unlucky, blow-by) but more often they just go bad and need replacing.  Thankfully the on-board diagnostics will tell you which cylinder is misfiring, making diagnosis easier.  Most people with tuned 1.8T's in their cars carry a spare coilpack or two in the trunk, as higher boost levels tend to kill them faster.

Of course, coil packs are a minor if annoying problem.  The real issue is oil sludging on Passat's and A4's.  Many have said that the 1.8T was designed with too small of an oil capacity.  Although 4 qts is normal for a 1.8L engine, one with an oil-cooled turbocharger (as well as an auxiliary oil cooler) generates a lot more heat, and more of the oil is circulating at any given time than a naturally aspirated engine of the same size.  So it's the same story with a lot of the other sludge cars on this list; if you mostly do stop-and-go driving where the oil never gets all the way to temp, the oil will break down, sludge, and clog the pickups and channels.  Oil pumps also have a tendency to go bad early on these front-to-back 1.8T's, which cause similar engine failures.

What to do?  Well, change your oil before the factory 5,000 mile interval.  Use API-certified 5w40 synthetic fluid.  Use the later-style higher capacity oil filter that lets you fit another half-quart in the system.  Don't get into boost when the temp gauge hasn't gotten up yet.  Don't flog the snot out of it then shut it off.  It's common sense.  With proper maintenance (and cam-belt and water pump changes at 60k!  5-valve aluminum heads aren't cheap!) a 1.8T will go pretty much forever at high boost on stock equipment.  If only the same could be said of it's bigger brother...

Audi 2.7T (B5 S4, allroad Quattro 2.7T, A6 2.7T)

This is what I call a bummer.  The 2.7T, you see, is an awesome engine.  Small all-aluminum V6, 5-valve heads, twin low-inertia Garrett turbochargers.  They make tons of torque stock, and have absolutely crazy aftermarket potential.  2.7T's have been kicking ass and taking names since they came out.  But buyer beware: Audi's twin-turbo wonder can suck your wallet dry with little warning.

You see, the 2.7T used two BorgWarner K03 turbochargers, one on each side.  These tiny little things are surprisingly robust on the 1.8T motor, but when they're crammed in a B5 A4 engine bay between the manifolds and the shock towers, they get very hot.  The B5 S4 had perhaps the most crammed engine bay you could possibly imagine.  It makes a Passat W8 look easy to work on.  And with owner neglect (infrequent oil changes, low oil level, shutting the motor off and stopping oil flow when the turbos are still hot), an S4 will chew up a turbo or two pretty early on.  Dead turbos on an S4 at 60,000 miles are not an uncommon occurence, especially if the engine is modified and running higher boost levels (which they usually are.  Come on.  Who wants a stock S4?)

The problem isn't as prevalent in the larger A6 and A6 allroad Quattro, since they have more room in the engine bay and generally aren't beaten on like a red-headed stepchild.  If you're thinking about buying a B5 S4: make sure it's got receipts for oil changes, and it doesn't sound like a dremel tool when hitting boost.  Or better yet, get an E36 M3.

Subaru SVX

"Subarus are like the AK-47's of cars.  They're cheap, unrefined, but they never break and they're easy to fix when they do."  Well, sort of.  Most Subarus will, with proper care and maintenance, give you a few hundred thousand miles of problem-free driving.  They'll vibrate till the dashboard rattles, the windows clatter every time you close the door, and they sound like tractors, but they're tough.

So when Subaru came out with a top-of-the-line luxury GT coupe in the early 90's, Subaru buyers were expecting more of the same usual Subaru reliability.  The SVX had a big flat-six engine, four wheel drive, and swoopy bodywork (with weird split-windows) designed by Guigario.  It also had a ticking time-bomb of a transmission.  The SVX used the same Nissan-derived 4-speed automatic from the 4 cylinder Legacy sedan, only it was hooked up to an engine with two more cylinder, almost another liter of displacement, and about 100 more horsepower than the Legacy.  You see where this is going.

SVX and Transmission Failure are terms that seem to go together like peanut butter and jelly.  The problem is heat, although it's exacerbated by a number of design flaws that Subaru continually addressed over the life of the car.  The SVX had a transmission cooler, but it wasn't efficient enough to keep temperatures in a safe operating zone.  Fluid flow through the transmission was less than idea, with a small mesh filter installed in-line that would eventually clog and block flow.  The final drive ratio was unusually high, leading to torsional stress on bearings and more heat.  The gasket on the fluid pump failed frequently in earlier models, which would lead to incorrect line failure and overheating.  It's just all bad.

How do you avoid the problems associated with the SVX transmission?  Well, some would say you should just avoid the SVX.  If you have your heart set on a funky split-window Subaru Coupe, then an auxiliary bypass transmission cooler will lengthen your tranny's life significantly, as will an external transmission filter that's replaceable.  Use only synthetic fluids and change them frequently.  But judging from personal experience (a friend of mine gave up on his SVX after it blew it's second transmission in a year even with proper maintenance) you might just want to avoid one.  Or, hey!  Maybe it's a good time for a big-turbo EJ257 and a six-speed.

3rd Generation Toyota Supra

It might be slightly unfair to categorize the 3rd generation Supra as entirely unreliable, but it does have one persistant, annoying problem: an insatiable hunger for head gaskets.  Of course it also had other smaller less important issues, mostly related to complicated and impossible to repair electronic components, but it was blown head gaskets that plagued the MKIII Supra from beginning to end.

The 7M was an iron-block straight six cylinder engine with a four-valve twin cam aluminum head, and it came in either naturally aspirated (7M-GE, Supra) or single-turbo (7M-GTE, Supra Turbo) form.  Both versions are equally likely to blow head gaskets, and a lot of Supra folks say it's actually due to improper torque on the head bolts from the factory.  Of course, being an aluminum head, if the engine overheats and the gasket blows, the head and the block usually need to be machined to spec so a new gasket will fit.  It's also suspected that the stock top-to-bottom torqued head bolts will stretch and loosen with age, speeding up head gasket failure.

Solution?  If your head gasket is fine now, make sure and tighten down the head bolts to perhaps 10lb-ft past factory specs.  If your head gasket has already blown, there's a fool-proof way to make sure it'll never happen again.  APEX-i sells a 1.2mm metal head gasket for the 7M that's a lot tougher than the Felpro or OEM gaskets.  The head has to be milled to spec for it, so while you've got it torn apart, replacing the factory bolts with ARP studs and caps also lessens the chance of the top going pop.  Then crank the boost and enjoy your Supra.

Porsche 986/996 Boxster/911

And we reach the end of the list with one most people don't know, or really even want to hear.  The fact of the matter is that early water-cooled Porsche Flat-six motors are pretty much junk, an expensive game of automotive Russian Roulette that most owners don't even know they're playing.  Problems are multiple, serious, and ugly.  TTAC's Jack Baruth has spoken at length about how terrible the early waterboxers are, and even I found a lot of it to be a bit scary.

The 996 generation 911 was the first big change for the 911 since...  well, since 1964.  The Flat-six engine gained water passages and a radiator, much to the horror of the Porsche purists.  But the level of cheapness built into these engines was even worse than the "is this a Porsche?" driving feel.  Here's a short outline of things that might have gone wrong with your brand new $75,000 911 back in 1999.  (Main points taken from a fantastic article by Total 911.  Fantastic read.)

  • Intermediate shaft failure.  This part runs under the block, driven off the crank.  It's what turns the cams in both cylinder heads.  The sprocket on the end of this shaft is retained by a small stud, which will break and cause the bearing that the sprocket rides on to fail as well.  It'll start out as a rattling noise and end up with the timing chains coming off, and both heads gathering a few expensive built valves.  Fix: rebuilt heads, new sprocket, new bearing, new stud.  Or a new engine!  $15,000.
  • Cracked cylinder heads.  Due to a design flaw in how the tappets bolt down, the heads might crack, allowing oil into the water jackets.  Which makes oil sludge.  Which kills the crank bearings.  Which means a new engine!  $15,000.
  • Cracked cylinder linings.  The cylinder linings start as two parts, and the aluminum block is cast around them.  The block itself is less rigid than the old air-cooled blocks, and under heavy load it can deform and will develop cracks in the cast-in liners.  This leads to coolant in the cylinders, and worst-case scenario, it causes the engine to hydro-lock, bending rods and breaking pistons and deforming the cylinders.  The 996 motor doesn't have individual, replaceable cylinders like the 993 did, so the whole cylinder bank is ruined.  You'll need a new engine!  $15,000.
  • PCV failures will suck oil through the intake, gumming up valves, sludging the oil... you know.  This might not require a new engine; breathe a sigh of relief.
  • Variocam (VVT) controller failure can lead to poor performance or a rough idle.  Thankfully this won't kill your engine!

Now, it's estimated that these failures only affect about 5-10% of early 996 (and 986 Boxster) production.  Which doesn't sound too bad - but if you knew your $75,000 Porsche had a 1 in 10 chance of needing a new engine at huge expense, how interested would you be?  What's worse is that Porsche spent more effort trying to pin the failures on owner neglect or abuse than trying to restore customer goodwill.  When the problems are clearly due to design flaws, the best strategy is not to insult your customers and assume they're stupid.  There are ways to avoid these problems, mostly aftermarket or updated OEM parts from later cars.  A better way?  Get a GT3 or a 996 Turbo.  For one thing, they're awesome.  But they also use the older 911 GT1-derived block that's not a split case, and these motors are almost bulletproof.

So next time you're car shopping, keep in mind that just because a car has a reputable badge on the hood doesn't mean it won't give you problems of some sort.  Do your research first, so you don't have to learn of a problem the hard (read: expensive) way.  Until next time, friends!

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