Engines! We expect them to do so much these days. We want them to fling us around on our errands for hundreds of thousands of miles, sipping the bare minimum fuel all the while. That’s simply the bare minimum these days, but some engines fail to meet these demands in a grand fashion. This leads us to our question today—what’s your most hated engine design flaw?
Try as they might, sometimes automotive engineers get it wrong—and an engine ends up with a fatal flaw. Months or years down the track, a poorly designed part lets go, or wear hits some critical point. Suddenly, dealerships are getting bombarded with calls, forums are melting down with rageposts, and the automaker is left to arrange repairs via an expensive recall campaign. Or, hell, even buybacks!
You would think that automakers would catch these problems in testing. After all, new engines and new vehicles typically go through millions of miles of testing before they ever hit the road. And yet, somehow, this still happens every few years, even to automakers with the best reputations for reliability.
Earlier this week, we were talking about a controversial example—that of the Cummins 6.7-liter diesel. Listen to some, and they’ll tell you the engine will gladly ingest a poorly-placed nut, munching itself to destruction in the process. Listen to others, and they’ll tell you it’s an incredibly rare ocurrance. It might have never led to a recall, but it’s a compelling tale nonetheless.
Other situations are more cut and dried – for example, when Oldsmobile engineers tried to make a diesel out of an old gasoline V8. That engine had drastically underrated head studs that meant head gasket failures weren’t just a possibility, they were a near certainty. Because of that decision, many car buyers saw diesel as a devil fuel in America for the best part of a decade afterwards.
You might also tip your hat to Lancia. The company famously built an engine so fragile that you could destroy it with a simple turn of the steering wheel. Properly Italian motoring, right there.
We love digging into weird engineering topics, and often it’s the quirky little failures that excite us—and you!—the most. So do tell us—what engine is your bugbear, and what is its fatal flaw that should never have made it to production? We’re absolutely dying to know what has your motor dying. Sound off below!
Credit: GM, Cummins, BMW
Any engine with a timing belt 😛
Well aside from what people already mentioned, I’m gonna mention the issues surrounding the Ford 5.4L 3V V8
Stupid 2-piece Spark plugs breaking off in the cylinder head
Cam phaser issues
Timing Chain tensioners
…and other issues. This is a good video on this
https://www.youtube.com/watch?v=wVFr4iF-ubA&t=33s
Also… the inadequate head studs on the GM Northstar V8 that went on for years before GM did anything about it.
https://www.youtube.com/watch?v=A1vc1-D1kXs&list=PLh3LJqzACNaN3lKVyTK7vRD47A7KXwBya
Chrysler PentaStar 3.6 V-6 has a plastic housing for the oil cooler and filter housing mounted in the V of the engine.
There are plastic push in pipe plugs for unused ports.
As the unit thermal cycles over time the housing fails or the plugs fall out causing complete loss of oil pressure and immediate catastrophic engine failure.
There are several inexpensive aftermarket replacements made from various metals yet Chrysler continues to use the plastic parts.
A sad situation for a company that was founded on advanced/superior engineering.
And presumably if you buy one and immediately replace those vulnerable plastic parts with more robust parts, then you’re voiding the warranty…
Don’t forget the plastic coolant connectors on the minivan engines. Ours somehow lasted 140000 miles before splitting.
I’ve had 3 pentastar v6s all with over 150,000 miles. Only had to replace oil cooler once and is was because the coolant weeping. Wasn’t a hard job either. I think this is an issue that has been overblown.
How about BMW and their Nikasil cylinder lining?
Don’t know anything about them putting that in cars, but my ‘82 R100CS had Nikasil linings. There were 3 things wrong with that bike, and that wasn’t one of them. The problems were 1: Exhaust valves or seats (forget which) were too soft. This resulted in them slowly receding into the head over time, you generally had to loosen them every time you did a tune up. Replaced valves and seats eventually, problem solved. Problem two: I never got the pushrod tubes to stop leaking for more than a month or two. There is a special tool for whacking them tighter into the crankcase and getting them to seal a bit better, but they always work themselves back out. Problem 3: Alternator too anemic to compensate for the amount of energy required by the starter, causing batteries to need constant trickle charging (and frequent replacement at $100 a pop in the 90’s). Kick starters did exist for that transmission, but it’s extremely rare.
BMW didn’t factor in the higher sulfur content for the US market. So, BMW had to replace many of V8 engines and revise the material contents.
Chrysler cloud car head gaskets. My dad had the head gasket replaced three times, every 18 months or so, on the ’96 Stratus he had. It wasn’t until the third one, where Chrysler finally introduced a redesigned gasket, that the issue was finally sort-of fixed.
Luckily the first one was replaced under warranty, but the second and third were on my dad’s dime. Which certainly sucked, not to mention the other issues.
Not a specific manufacturer but the recent advent of direct-injected engines without a solution to keep the intake ports clean. PCV system eventually creates heavy carbon deposits, which in addition to restricting airflow, eventually fall into the combustion chamber and plug up the piston rings, causing them to get stuck and eventually burn oil, even on an otherwise well-maintained engine. Of course, this issue tends to become noticeable around the end of the typical warranty mileage limit, go figure.
Just seems so backwards to me that with a century of engine development we have gone back to engines that burn oil.
And the worst part is the solution is extraordinarily easy, it just costs money, which is some semblance of port injection. The extreme of this that’s downright maddening is North American market Mk7 Golfs of all trims save TDI have Direct Injection only engines. The exact same models with identical power specs in Europe have dual injection, therefore not requiring a 60k interval for intake manifold cleaning. There are even retrofit kits for USDM Mk7 engines available that use almost entirely OEM parts.
lol that is crazy! Hard to believe because usually a manufacturer pulls a stunt like that to save costs on something that isn’t required (even if it is a really good idea to include). I cannot imagine EU requires this solution. Compare this to Hyundai which didn’t include an immobilizer on their US vehicles because USA doesn’t require it, whereas Canada does so Canadian models have it.
I’ve only got two guesses, one more favorable than the other.
1 is that EU emissions standards being stricter than the US means that the port injection supplement have some minor benefit, that and that the European market is accustomed to spending more on VWs, so it’s an acceptable extra cost, or that it’s cheaper to sell them in Europe than in the US
2 is that they realized they could get away with it in the US and squeeze some margin out of their USDM lineup. Knowing modern VW, this seems likely, but is deeply frustrating.
DI only is not nearly as frustrating as the horrible gen3 EA888 water pump design that fails constantly on Mk7s. My ’18 Golf Sportwagen threw a low coolant warning the day before I traded it in on my CX-30 with 56k miles in late 2022. I consider than completely unacceptable on a modern combustion engine, especially on one that’s so widespread with so many model years to remedy the design.
As the kids say, why not both? Both #1 and #2
Had two Focuses, one DI and the other turbo DI, over 200k and 180k miles respectively without any loss of performance, mileage, or drivability and no maintenance beyond oil changes and spark plugs every 75k. The first car ran like new when it was totaled and the other had the Ford Ecoboost 4 cylinder coolant issue, but it was perfect until that happened (and really, it still ran fine and cool even with the cloud of smoke out the back). Don’t know why the German and Korean cars had issues with it, but they have issues with just about everything and, hell, if Ford of all companies could get it right, it’s not the technology. That said, I do feel better having dual port and DI injection now.
There is always the Ford Triton V10 (the earlier ones) that has a fun habit of popping spark plugs out of the block (including the threads of course). Anytime you have an aftermarket that comes up with whole kits with dedicated tools designed to repair an issue, you know it’s a design flaw.
There is also the Ford 1.0 Ecotec with the belt drive oil pump that likes to prematurely eat the belts.
It wasn’t just the V10’s, it happened in both the 4.6L and 5.4L V8’s…
I can definitely confirm it happens with the 5.4’s never had a 4.6. My 5.4 Expedition was also constantly blowing coil packs…. It only ran on 6-7 cylinders for most of the time I had it… I had a bar welded in for the plugs, after I fired 3 out of the block, but that didn’t stop the coil issue.
That happens on the V8s and v10s, only 2006 year and earlier. Allegedly it can happen on 4.6s also, but that seems to be massively rare than on 5.4s.
Anything with a plastic water pump impeller. VW and BMW are the worst offenders to my knowledge.
Plastic timing chain guides are a close second.
‘Lifetime’ fluids on transmissions (I once heard some US market yugos didn’t have engine oil drain plugs!?)
Timing systems (belts or chains) that require removing the engine to service
Almost all timing chain guides are plastic.
The surface that the chain rides on is almost always plastic (for good reason, you don’t want metal-on-metal contact in that situation), but the body of the guide is often metal, which makes it much less likely to break off the fasteners or snap in half (which generally leads to catastrophic engine failure)
Too many to name, so I’ll go with the one that hit me personally: Ford 4-cylinder Ecoboost closed deck engines. Still not exactly sure the cause of the problem, but something about the cooling passage between cylinders 2 & 3—presumably on the block side since the only approved “fix” is engine replacement—fails and causes coolant to get into the cylinders. Several CA suits about it and it seems to effect all displacements with the closed deck that I bought thinking I wouldn’t have to worry about a bad HG. At least I got 180k trouble free miles out of my Focus ST befoe it went, unlike many other people who had theirs fail a lot sooner, some right out of warranty. If we were going to go with an engine branding that stands out for being terrible, I’d nominate Ecoboost as I think every damn type and cylinder count has some big problem.
I only got 73k miles out of mine before this happened earlier this year to my Edge that we bought new in 2017. Ford did help soften the blow, so I do give them credit for stepping up. But the engineers that approved this cooling design should be publicly shamed.
The copper cooled Chevrolet they made 300, sold 100 and managed to recall and destroy 98 of them
Anything with a timing belt.
As long as it’s not paired with an interference engine design, I have no problem with timing belts. They don’t seem to cause any more issues than timing chain designs that develop slack and start eating through things/slipping gear teeth (often due to plastic guides failing admittedly)
Problem is, the high compression ratios needed to meet modern emissions standards have all but killed non-interference designs. There just isn’t enough space in the combustion chamber to avoid it.
Back for more I see…
Much like with Jeeps, David doesn’t learn from just one mistake…
4.0 AMC straight sixes with bad castings.
(I’m still bitter about you impugning the reliability of my J35s.)
Laughs in 2UZ-FE (also 1 and 3-UZ), and the 1-2JZ, etc.
Define reliability differently. If timing belts routinely gave out in less time than their expected 7yr/100k life span (using my Honda V6es as an example), then we’d say they’re unreliable. But they don’t. We know how long they last, generally, and can be prepared for the cost or weekend of time.
But what’s another wear item that is expensive (can run up to and well over $1k), MORE exposed to potential damage, lasts maybe half the time of the typical timing belt (though this can be far less depending on driving style), and can only be replaced by a specialty shop with tools most shadetree mechanics don’t have?
Tires. You going to tell me now that a car with tires isn’t reliable? I reckon we better hurry up and get the twheel into mass production, then!
Just because you say that your engine is going to blow up at 90K miles unless you do something about it doesn’t mean it’s acceptable that the engine blows up at 90K miles.
It’s a service item, like oil, or spark plugs, or pistons on a 2-stroke. Change them when you’re supposed to and it’s reliable. Don’t change them and it’s not.
Personally I prefer gear driven over head cams. That whining noise at 14,000 rpm is great. But a cam belt isn’t inherently a flaw.
Having to take an engine mount off to change a cam belt is maybe a flaw, but then there are engines out there that have to be removed to change a spark plug, and that doesn’t make all spark plugs a flaw.
I thought you might say this. Maybe you knew that the QR and VQ line of engines from Nissan use the very reliable timing chain? And perhaps, you know that you can get those engines bolted to the irrefutably best transmission ever made, which is of course the Jatco Xtronic CVT. What better combination than an engine with a worry-free timing chain and a transmission with worry-free lifetime fluid?
Are we ignoring the Porsche IMS bearing because it’s common knowledge now?
Nobody remembers the Ford 3.8L Essex engines? The ones that routinely blew head gaskets? And often came attached to notoriously unreliable AXOD-family transmissions? Multiple design flaws involved there.
3.8L head gaskets were pretty bad, except on the T-bird super coupes since those had a better designed head gasket (copper i think?). Agreed on the AXOD/AX4S/AX4N family of transaxles… they weren’t the worst… but they were far from the best.
Not the worst engines ever made. The engine was good to drive until it expired.
But the 3.8/AXOD combination made for a potent combination of drivetrain issues. Taken together, the drivetrain belongs toward the bottom of the list.
The Thunderbird SCs ate head gaskets like like a football team eats at a buffet. Take the same head gasket design and pressurize it, then add a spot in the exhaust that raises backpressure. Bad news. I was very lucky that mine didn’t go.
The cure was a Fel-Pro gasket that was WAY better. Some thought the answer was to eliminate the backpressure issue with a new resonator that didn’t kick down a half inch to limit horsepower.
I should add that Ford spec’d replacing the sparkplugs as an engine-out job.
I was gonna mention the Ford 3.8L… though they did eventually fix the issue in the late 1990s by switching to MLS head gaskets.
I’m surprised I haven’t seen mention of this one yet : the GM/Detroit Diesel 8.2 “Fuel Pincher”.
Such a POS that most of the engines production run was to make spares for the ones that were actually still running. And they were in medium duty trucks, in other words, people who can’t afford downtime. It made the Olds diesel look like a Toyota motor.
This is a really good take. The 8.2 Fuel Pinchers were so bad, they are basically all gone, and there isn’t a ton of info out there on them because of it.
Internally at the General these were known as the “Blue Plague” based on their paint color.
GM had built heavy duty 2-stroke diesels for trucks, buses, and locomotives since the 1930s and they were struggling with emissions and fuel economy vs the 4-stroke competition.
The 8.2 was an effort to get into the medium duty market with a 4-stroke design that didn’t really have the required durability.
They eventually got it right with the Series 60 nearly 10 years later.
Ford Cyclone 3.5/3.7 V6 Water Pump Location and Failure! To make the Cyclone V6 fit in FWD/AWD vehicles, the water pump was relocated internally! (Brilliant move, it’s not like you’ll ever need to replace it or anything, right?) To make things far more complicated, they also used the timing chain to drive the water pump.
Timing chains stretch (especially the ones FoMoCo seems to use) and over time the bearings in the water pump wear out. The water pump eventually fails and the end result is coolant leaks into the crankcase and turns the engine into a boat anchor. Best case scenario, replacing the water pump costs around $2,500 (12-14 hours of labor).
The sad thing is there are millions of these ticking time bombs out there. My mom’s 2012 CX-9 is among them and it’s only a matter of time.
If you change the oil more aggressively than the oil life computer determines – which is up to 10,000 miles! – the timing chain stretch issue is greatly mitigated. One of my buddies oversees a fleet of Explorers and Tauruses (those that remain, RIP) with them and they do oil and filter changes every 6 months or 6,000 miles, whichever comes first, and they always check the weep hole to see if the water pump has developed a leak. To date they’ve had one failure, but supposedly the user was idling for much longer than reported running the A/C the whole time.
As for the water pump job, your $2500 figure seems a bit high for the Ford motors. It’s a 3.7 hour job if caught early for just the water pump, or 8.7 hours to do the chains including replacing the camshaft sprocket on a NA AWD setup. Even at $200/hour that’s only $1,740.00 in labor, so about $2K with parts.
Now if it’s an EcoBoost, yeah, it’s a 10.6 hour job to do the chains, but – again – this can be mitigated with aggressive oil changes and proper inspections.
CX-9 is a slightly different animal. The 3.7L does have to be dropped to do the chains in those, but they don’t seem to have the failure frequency that the Fords do, likely due to the lower oil change interval set from the factory, which I think was 5,000 miles (maybe 7,500). So, yeah, 14.5 hour job, plus parts. Not a fun one. In contrast, doing the chains on the same engine in the Edge is a 11.9 hour job (drop not required), 12.4 in am AWD Lincoln MKZ, and so on.
Asshole dealerships, like Lewis Ford in Fayetteville, AR, will quote you $1875 for the chains, pump and everything else on a SHO with the 3.5 ecoboost. And when you go to pick it up? How about nearly $3500. Oops!
There’s a reason why they went to an external water pump and both port and direct injection when they put it in the F150. Just a shit design.
And, btw, I always change the oil at 5k miles with Motorcraft parts. Shit design.
Distributor mounted underneath and between the water pump and engine block.
Ah, the Optispark! I had one go on my Trans Am. Not only is it an incredibly poor design, you can’t buy decent replacement parts anymore unless you’re willing to pony up for an expensive version from MSD.
Dumb design but the 4th gen fbody has that radical windshield rake. Which puts the back half of the engine under the cowl. Which is where the distributor goes on a small block Chevy. It wouldnt fit. Thus optispark. Still seems like a kludge of a design though, dont know why they didnt do coil on plug igniton(Buick started doing that on the turbo 3.8 V6 back in 1984 or so)
in theory it was a fresh and compact design to accompany the reverse flow LT1. It actually works fine if you keep water out of it. and the 95-96 design had the intake sucking air out of the thing versus just weep holes so that technically worked a little better, but yeah they definitely could have done fine with a timing wheel on a flattened shell of a distributor like they did with the 4.0 HO straight six in 96. and then mounted a bank of coils out of the way.
It would have been nice to mount the water pump under or tot he side of the optispark though. when you change the water pump since it was just above it on the front, it always took out the optispark when even a few dribbles hit it.
Transversely mounted Duratec V6 engines with the water pump buried behind the timing set(also they seem to like to put the oil filter directly above the exhaust Y-Pipe on many of these, so there is that little gem). Followed closely behind the DOHC 3.4 V6 from GM with the alternator buried behind the engine but down so low that outside of removing’s an engine bone and rocking the whole mess forward, you are just never going to get that thing out.
I’m surprised at the chirping the Duratec and Cyclone are getting. Yeah if the driver neglects oil changes and the tech doesn’t notice coolant coming from the weep hole they can turn into problems, but nothing near as bad as the 3.6L “High Feature” gm engines, or even the 3.6L Pentastars in Mopars.
Are they as relatively reliable as the 3.5L Toyota/Lexus V6? Perhaps not, though those also have more aggressive oil change intervals which helps their longevity. And THAT water pump is a true pain to do (and the shape is also humorous on a sophomoric level).
At least they have chains instead of a belt like the Honda 3.5L, right David Tracy?
People don’t catch the weeping until it manages to pool up enough to get past the belly pan and leave a mark on the ground. generally by that time the crank case has already started getting coolant from the second seal also failing. so yeah if you catch it the cost is only a cool 2 grand for a new water pump. if you did not catch it the whole engine is a milkshake and you may not have a clue why since it was not showing head gasket signs, but the damage is done internally. I actually figure the F150 would not be designed differently when I found out about this design flaw on the transversely mounted set up….but guess what. some F150 Engineer caught the problem and did not allow it to get to the Jewel of the ford line up.
I came here to post about the Duratec V6! The alternator takes 6 hours to change per the book. It also takes 6 hours to change with TWO experience shade-tree mechanics.
Why?
The alternator is mounter on the bottom passenger side of the engine. You need to:
It was an absolute pain in the ass.
Caused me to pretty much swear off ever owning another transverse v6 or v8 car.
“a 4 foot socket extension is required” wow
Duratec V6 ALSO mounts the alternator back there. Ask me how I know!!
Any thing that is billed as being a non-service component.
BMW N63. Early versions were a mess.
As a previous N54 owner who spent lots of time in the engine bay, it always amazed me how much stuff was plastic that shouldn’t have been (charge pipe) and how despite making the same straight 6 engine for decades, somehow BMW always find a new way to make it unreliable. Truly an impressive engineering feat.
Knowing how bad the N62 is (leaky valve stem seals in particular) and how bad the N54 is (not internally, but everything bolted to it), I can only imagine how bad the N63 must be.
Hydro lock due faulty injectors. This bad.
Wow. That’s N62 to the N54th power bad.
Well, given that my truck is currently still sitting in South Dakota due to a failure of the tone wheel that the crank position sensor reads, I’m gonna have to go with that one. It’s common enough that they did a recall so the truck wouldn’t immediately shut off when it happened, and I actually saw one guy on the forums celebrating because his died during the extended warranty period. Lucky bastard.
Oh, and the icing on this shit cake (and the reason I still don’t have my truck back) is that despite this being an extremely common failure, they somehow don’t bother to stock the parts to fix it so I’ve been sitting around for a month waiting on backordered parts. At least they finally came in today.
What truck is this?
Oh, hah, I never did say, did I? It’s a Ram Ecodiesel.
Ford Motor Company.
General Motors.
I’ll second Generally-problematic Motors. Seemingly more misses than hits (especially the last few decades), despite their allegedly vaunted reputations (which I don’t understand).
The mid-to-late 90s 2.4 Quad4 from GM had a pretty high head gasket failure rate in my experience. I am not entirely sure why they failed so easily, but most people I knew who decided to get a Grand Am/Grand Prix/other cheap GM car with them in the early 2000s had a head gasket failure pretty soon after buying it.
Also, a shout-out to the GM 3400 V6s for their intake gaskets failing and contaminating the DexCool coolant, turning it into a brown sludge. I saw the aftermath of a failure on a late 90s Blazer when I worked at Canadian Tire; one of the mechanics grabbed me from the parts counter and said “You’ve gotta see this!” The radiator looked like an elephant had taken a massive diarrhea dump into it, and it needed pretty much an entirely new coolant system.
It wasn’t just the 3400s, I had a 3.1 litre V6 with the same issue.
it was more of an issue in the 3.4’s at the turn of the century. they even made a service bulletin and revised intake gasket, but quietly told no one in hopes the crappy ones would make it past the warranty period.
Dexcool in general could be touted as a bad design Idea.
I’ve never understood the hate for Dexcool. I’ve had dozens of GMs with it including several well over 150,000 miles without cooling system issues. The manifold gasket leaks would have been just as disastrous with common spec antifreeze.
Those manifold gaskets were a serious problem and happened because of incompetent people in GM Powertrain who screwed it up initially and refused to change after being presented with volumes of failure data.
the 3.4 intake design for sure was on GM. Dexcool mostly gets a bad rap because someone unknowingly mixes something else in the system, causing all sorts of incompatibility issues. That being said the Dexcool does in fact break down on it’s own in as few as 2 years and the result is a corrosive material afterward. I suppose if you flush the systems regularly it would be fine, but what is the benefits outside of just using good old Ethylene Glycol?
I never had a head gasket issue with my Q4HO, but it did have the exhaust cam gear bolt loosen up and eventually snapped the dowel pin on the cam at about 4,000rpm. Every exhaust valve kissed a piston..
Disintegrating plastic timing chain guides are an annoying problem on many engines from many brands. The one that comes to mind is the Nissan VQ35.
Not even having experienced one (that I know, anyway), this is immediately what I thought of when I read the headline.
I just looked up the QR25DE in my beloved Sentra SE-R Spec-V and it had them. Damn. Still though, 247k was a hell of a run.
How about the Chrysler 2.7 liter V6? That engine had a fatal flaw where sludge would get trapped and eventually lead to the engine grenading at 100K miles or so. I had a 1998 Intrepid and did everything I could to keep up on the maintenance including using synthetic oil. None of that mattered as the engine died at 125K. Maybe I just prolonged the inevitable.
Maybe not as bad as the Vega engine though. I remember my Dad complaining about that one as a kid. We didn’t even have a Vega but Dad hated the engine enough to keep complaining about it.
Against all odds, our 1971 Vega gave us 125k trouble-free miles (no head gasket or oil burning issues) before it disintegrated into a pile of rust.
GM 6.5 Diesel with the block casting flaw on every single engine.
Hyundai’s 2.0 and 2.4L engines that like to explode at crazy low mileage.
Toyota’s piston ring fiasco on early/mid 2000s 2.0 and 2.4L engines. A friend of mine has one of these and it drinks oil like a sailor on shore leave even though it only has 134,000 km on it. Even though there was a recall Toyota said her car is too old to qualify for the recall.
All 2.0T VAG engines with the plastic timing chain guides.
Agreed on the 6.5 Diesel…blocks crack, PMD issues, etc… But beyond that.. they came out with the 6.5L Turbo in what, 93? Upgraded it to electronic injection a year later, but it was still an outclassed, out of tech piece of shit within 12-18 months when Dodge had the direct injection 5.9L and Ford had the direct injection powerstroke.
GM hung on to that dumb IDI motor that was low on power AND low on reliability for customers who demanded both all the time.
Which is such a shame! Because GMT400s were incredible trucks for the time.