Home » Plastic Underbody Shields Are The Shame Of The Modern Automotive Industry

Plastic Underbody Shields Are The Shame Of The Modern Automotive Industry

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I’m willing to bet genuine, damp money that this has happened to you or someone very close to you at some point: on your car or one of your cars, likely one made in the past 20 years or so, you’ve noticed an annoying flapping sound or a scraping sound. It gets progressively worse and is louder and more annoying the faster you go. It’s awful, and by now I suspect you know exactly what it is: big hunks of plastic coming loose from under your car. These plastic sheets and panels are sometimes known as splash shields or aero shields or underbody shields, something like that. They’re also one of the worst-engineered components of modern cars and are a global embarrassment that so far no automaker seems remotely interested in doing anything about.

Years ago, I wrote about what I felt was one of the biggest engineering failures in the automotive world, the scourge of sagging and falling headliners that plagued cars from the 1970s to the 1990s. I think the industry-wide epidemic of falling splash guards easily meets or even exceeds the Great Headliner Failure of decades past; the problem crops up on cars all across the automotive spectrum, and doesn’t seem to be restricted to inexpensive cars. Premium cars seem as likely as any to have their underbody plastic sheeting tear and break loose, which gives the problem a nice egalitarian character, at least, as likely to plague Mercedes-Benzes as a Hyundai.

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It’s probably worth mentioning just why these shields exist in the first place, and there’s a number of very valid and reasonable explanations. They provide some aerodynamic benefit, helping to smooth out the path of airflow under the car, they prevent water and dirt and grime and other crap from being flung up into the engine bay, where it could potentially cause electrical issues or increase wear on belts and hoses, and, well, I suppose that’s pretty much it. They provide some degree of protection from scrapes and bumps, but they’re not actual skidplates, so your oil pan may still be boned if you whack it hard on a rock, plastic shield or no.

I was going to provide some links to people talking about the issue of loose or falling plastic shields, but a bit of Googling soon revealed the folly of that idea, because there are so many examples. If you just type into Google the words “plastic cover under” – not even mentioning anything about a car – you get results like this:

 

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Look what you get: loose, fell off, came off, hanging, dragging, the state of plastic covers under cars is not a good one.

I tried one with a normal browser window and one in incognito mode, just to be sure the suggestions weren’t influenced by my previous search history, and, as you can see, even without specifying car, Google knows what’s going on, because vast numbers of people have been asking these questions, since these stupid plastic shields have been tearing off cars all over the place.

The reasons why this happens isn’t exactly rocket surgery: the plastic gets worn and tears, especially around the points where the plastic shields actually attach to the structure of the car, where it’s usually secured with plastic clips and tabs and other bits of degradable, consumable hardware. Plus, many of these shields require removal to do basic maintenance like oil changes, and that increases wear and tear on the too-fragile fasteners that hold these things on.

They’re also usually a pain in the ass to get out of the way when you just want to change your oil, and I suspect many get ripped out in during these processes.

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Tomorrow I’m supposed to help a friend remove one of these shields from her Honda Fit; it’s one I’ve repaired with zip ties before, and I can’t even recall just what number of times I’ve done exactly this same job – ripping out a raggedy splash shield – for one of my own cars or a friend’s car, often done with some amount of frustration and anger in a parking lot, at night.

If your car has these plastic shields, it’s not really a matter of if it’ll get torn and start flapping around, it’s a matter of when. These are not really a solved engineering problem, by any means. They all fail, and they all fail in essentially the same, annoying ways. The holes for the plastic fasteners rip, the panels themselves rip, everything sags and flaps and oh they’re just stupid and terrible and nobody likes them!

My older cars don’t have any of these things and they survive, somehow. And, I’ve yet to meet anyone who has yanked out big chunks of ragged charcoal-gray plastic from under their cars, flung it in a dumpster, and somehow regretted it. Once these things are ripped out, perhaps your highway fuel economy drops by half a mile per gallon, perhaps your belts get more wet than before, but generally, quality of life improves.

There have to be better ways to mount these things if they’re so important, but I doubt that will actually ever happen, because that would require more money to be spent. Fastener holes could be reinforced with metal grommets, or some manner of quick-release clamping system could be used to retain the splash guards, but is any carmaker going to invest more money to make that happen? I doubt it.

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From their perspective, this is hardly a problem at all. The shields start to fail long after the car has been purchased (generally) and the customer either rips the floppy plastic out or pays to have a new sheet installed. The carmakers have no downside here! This is just one of those side effects of capitalism where making something not suck just isn’t worth it, and the consumer can just shut up and deal with it.

But that doesn’t mean we have to like it! We can kvetch, loudly and boldly, and let the automotive world know we’re on to them. Underbody plastic bullshit is garbage, piping hot, cream-frosted garbage, and we’re doomed for the foreseeable future to have our cars, at some unpredictable, unexpected time start to make horrible flapping noises, requiring us to shimmy under the car and sweatily cut and yank and grab and pull out all of that near-useless, degraded plastic, and fling it into the trash, angry at the waste and senselessness of it all.

So, I’m calling this as The Biggest Modern Automotive Embarrassment. Plastic splash guards and underbody shields may be engineered for their purpose, but it appears no attempt is made to consider the longevity of these things, or how they may fail. And the result is hassle for pretty much every car owner, at some point.

Screw these things. We can do better. I have to believe that, I just have to.

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Space
Space
4 months ago

I would hate these less if the OEM offered a metal replacement for a reasonable price.

Daniel MacDonald
Daniel MacDonald
4 months ago

I’ve rarely bought a used car where these things weren’t a mess and sadly on at least one car I gave up trying to reattach the pieces and pitched it. I do think a big part of the failure is various accidental “off road” excursions or accidents conspiring with cheapy plastic fastenening mechanisms to contribute to a high rate of failure or at least high rate of raggedness.

Ben
Ben
4 months ago

Here’s an even bigger scam: They’ve started making splash guards out of porous material. Why, you ask? Because the porous material is better for NVH…right up until it gets saturated with water, at which point it’s worthless at best. I mean, who could predict that splash guards would get wet, right? I saw another comment mentioning that they also fall apart when they get wet, which is unaccountably stupid.

So it turns out plastic splash guards aren’t the worst thing ever. Fibrous splash guards knocked them off that pedestal.

Daniel MacDonald
Daniel MacDonald
4 months ago
Reply to  Ben

I’ve noticed that as I’ve been car shopping lately and was a bit flabbergasted. Seems like a bad idea, unless they’re somehow way more durable than they look. But as the article points out given the level of engineering given to their plastic predecessors no reason to believe the fiber ones won’t be crap.

Scott Wangler
Scott Wangler
4 months ago

My 2014 Ford Focus has 200,000 miles on the original panel and has proved to be problem free. I know sometimes they can be damaged by deep snow.

Ryan
Ryan
4 months ago
Reply to  Scott Wangler

The one on my Bolt disintegrated in the first winter of ownership. The tires kicking up wet, heavy snow was just too much for it. The rest of the broken one I removed was about 1mm thick pressed fiber. Mind-blowingly absurd that any level of validation showed that would hold up under a car in anything other than the mildest of climates.

Mashkhazamfahr
Mashkhazamfahr
4 months ago

These vary so much between manufacturers though. The removal as part of an oil change component makes the poorly engineered ones egregiously bad. My brother’s 2016 Q5 has a plastic aero shield that ties the bottom of the wheel wells to the car. It’s held on with 21 fasteners screwed into the plastic and requires 2 different types of tools to remove. And that’s required to access the drain plug. On the other hand, my 2014 Acura TSX has an aero shield that needs to be removed for oil changes as well, but only has 7 machine fasteners that go into machine threaded inserts so it’s very easy to remove without the possibility of stripping the threaded inserts.

Mollusk
Mollusk
4 months ago
Reply to  Mashkhazamfahr

BMW at least came up with the brilliant idea of putting a little door in the shield right under the drain plug. It’s hinged and opens with a quarter turn of one permanently affixed screw.

Daniel MacDonald
Daniel MacDonald
4 months ago
Reply to  Mollusk

unusually user friendly maintenance solution for BMW

Andy Individual
Andy Individual
4 months ago
Reply to  Mollusk

But you still need to remember the password and enter it in the OBD and you need a custom $450 driver bit for that one screw. And that’s the only fastener on the entire car that uses that bit.

BOSdriver
BOSdriver
4 months ago

These things are terrible. Over 15 years ago I was getting my future MIL oil changed at a shop where a cousin of hers worked. Luckily he recognized the car and put the shield back on. This shouldn’t be noteworthy but even back then the guys used to rip them off and throw them in a pile in the back of the shop.
Personally, I have dealt with a damaged one on my current car. Replaced one myself and had a dealer replace one after they messed up installing it after a basic repair.
The other thing that is annoying is that the guys, even at the dealership, use the wrong hardware to screw it back onto the car around the oil change access points. Horrible design all around.

Jb996
Jb996
4 months ago
Reply to  BOSdriver

Sounds to me like horrible dealership and oil change techs.

Red865
Red865
4 months ago

Not only under the engine bay, but additional panels under the cabin on my Escape. Only discovered this a week after I had some work done at dealer. Was doing 70ish on interstate on a windy day when all of a sudden car made this gosh awful roaring noise. Thought the transmission had just kick the bucket. Pull over and look under car…both plastic panels running under cabin were folded back in half with front edges ground off. Some tech forgot to put the front clips back in. They ordered new replacement panels.

Chrisjbuffy
Chrisjbuffy
4 months ago

Last time I changed my transmission fluid I spent more time trying to get the damn shield fasteners back on than on the actual job. Granted this was done withoug lifting the car, but still, such a PITA.

Thomas Benham
Thomas Benham
4 months ago

Preach it Brother Torch!
I used to be a VW parts guy, that stuff is nearly $300 on a MK4 Jetta and $700 for a B5 Passat.

The Artist Formerly Known as the Uncouth Sloth
The Artist Formerly Known as the Uncouth Sloth
4 months ago

uh, Torch? You feel well enough to go crawling under friends’ cars and tearing out their plastic undergarments?

755_SoCalRally
755_SoCalRally
4 months ago

My first thought as well. We need Jason hale and hearty in these dark times!

MiniDave
MiniDave
4 months ago

In my experience what causes these things to fail is lazy mechanics who can’t be bothered to install all the OEM fasteners after they have them off for service. Case in point, the wife’s Audi was only seen by the Audi dealer thru 6 years of ownership, once out of warranty I took over the servicing of the car – first time I went to do an oil change only 4 of the original 12 or so fasteners were still holding the damn thing on! I replaced all the missing fasteners and never had one fall out or come off in the remaining 12 years we owned the car. THAT’s the problem, not the plastic underbody shields themselves.

Obviously if you hit something or catch it on a curb when parking all bets are off.

Ryan
Ryan
4 months ago
Reply to  MiniDave

The one on my Bolt disintegrated in the first winter of ownership. The tires kicking up wet, heavy snow was just too much for it. The rest of the broken one I removed was about 1mm thick pressed fiber. Mind-blowingly absurd that any level of validation showed that would hold up under a car in anything other than the mildest of climates.

Spectre6000
Spectre6000
4 months ago

When I get a car that has these, they’re invariable missing a few fasteners. I just replace them, and have never ever had any issue with this.

Mr E
Mr E
4 months ago

And don’t get me started on those godawful plastic screws Ford uses to secure the battery cover under the cowl on modern Mustangs. Every time I have to jump a Stang in the showroom, at least one of them goes missing.

Perhaps the proliferation of EVs – with their range extending aero undercarriages – will finally sound the death knell for the plastic shit shields? One can dream.

VK
VK
4 months ago
Reply to  Mr E

EVSs? Seriously?

Iotashan
Iotashan
4 months ago

So, you’re saying that aftermarket sheet metal versions would sell like hotcakes?

NeverAgain4cyl
NeverAgain4cyl
4 months ago

Apologies sir but you are wrong.
The only reason these fail is lazy mechanics who fail to place back all the fasteners and careless mechanics who strip them with power tools.
Over 15 years and 8 Mercedeses (some of them high millage) never has one failed (All Mercedes underbody panels that are removed for service are to be held by 8mm rust resistant fasteners with giant washers as dictated by the German purity law).
Also note that in addition to increased fuel consumption there will be a significant increase in NVH (on the N side) if these are removed.

JumboG
JumboG
4 months ago
Reply to  NeverAgain4cyl

My BMWs of the 90s have shields with half turn Phillips head fasteners that stay on the shield when you loosen them. So you don’t lose them. The screw into metal clips, so you can’t tighten them so much that they break.

Contrast that with US domestic and Japanese cars. They either (Ford) have screws that screw into plastic inserts that strip out easily, or (nearly everyone else) use plastic pins and clips of varying sizes that are a PITA to remove, easily break, and are in so many different sizes the only place you can get them are individually at the dealership, or huge bulk packs online.

EXL500
EXL500
4 months ago
Reply to  NeverAgain4cyl

Mine failed multiple times entirely unrelated to having been to a mechanic for work.

NeverAgain4cyl
NeverAgain4cyl
4 months ago
Reply to  EXL500

Was it a Mercedes?

EXL500
EXL500
4 months ago
Reply to  NeverAgain4cyl

No, a Honda Fit.

Duke Woolworth
Duke Woolworth
4 months ago

We had a Mazda3 with the plastic underbody fastened with steel speed nuts, which quickly corroded in our road salt and made changing oil a real bitch. Zip ties to the rescue. After my wife hit a curb and tore the whole interconnected mess out including fender liners and $750 more pieces, we got the hint. My old time mechanic said the if you can’t see the street when you open the hood, pass.

Jb996
Jb996
4 months ago
Reply to  Duke Woolworth

On the other hand, my 2014 Mazda 3 is held on with galvanized bolts along the front, and plastic clips around the remaining sides. It has held up just fine and is in beautiful shape. There is one screw to remove the access panel for oil sump/filter.
The panels are there for aerodynamics and therefore fuel economy.
Does your old time mechanic complain about fuel-injection too? Electric radiator fans? Having to disconnect airbags?

Cerberus
Cerberus
4 months ago
Reply to  Jb996

Doesn’t seem like smart advice from a mechanic in the salt belt since these things have been very common for nearly, what, 20 years? How many cars predating that time are left in such an environment that aren’t falling apart and why would a mechanic want to work on it? Corrosion is easily one of the worst things to deal with when working on something and, when getting paid book, costs time (money) and often collateral damage the mechanic may have to eat.

Andrew Bugenis
Andrew Bugenis
4 months ago

My Volt has a fabric shield on the bottom. It stays on pretty well, but one time a fastener came loose and a bit behind the wheel was dragging on the ground. The tech just cut that part off, leaving the rest of it intact. I wonder if that’s better or worse; seems like it’d be a cheaper replacement part, anyway.

Jb996
Jb996
4 months ago
Reply to  Andrew Bugenis

Oh it’s worse. Far worst. A competent tech would have re-fastened the shield. I can’t believe he cut it off, permanently ruining your underbody shield, just so he didn’t have to find/fix a plastic fastener.

Andrew Bugenis
Andrew Bugenis
4 months ago
Reply to  Jb996

I suppose I misspoke; the fabric itself had torn around the fastener so a new one wouldn’t actually hold anything, so he cut off, like, maybe half a square foot.

My “better or worse” comment was about fabric vs. plastic.

Jb996
Jb996
4 months ago
Reply to  Andrew Bugenis

Got it. Makes sense.
I just get overly frustrated and a bit reactive about mechanics/techs.
Some are great, and hard to find.
Some cause more problems then they solve through “shortcuts”.

Jonathan Green
Jonathan Green
4 months ago

You ever drop a nut, bolt, socket, or other tool while working in the engine bay, and you think “no biggie, it’s under the car now, I’ll just reach under and get it”, and it isn’t there?

That is what these things are for.

Morgan Thomas
Morgan Thomas
4 months ago

Fortunately my 2003 Fairlane’s splash guard doesn’t need to be removed to change the oil or filter.

My Fiat 850 Series II Sport Coupe had covers enclosing the bottom of the engine bay – their main function was to ensure the hot air pushed forward through the radiator by the fan and then flowed down and out under the car wouldn’t flow back up into the engine bay. Fortunately they weren’t plastic, but pressed steel, with a rubber gasket to seal against each side of the sump. When i bought my Fiat one was missing, and it was a shape that would have been difficult to make from flat sheet. Luckily when I went to a local Fiat workshop they actually had a brand new one hanging in the rafters covered in dust as a result of hanging there for about 25 years!

Anonymous Person
Anonymous Person
4 months ago

Our 2003 GMC Envoy has a great under-engine shield. It has a very robust cut-out that opens with 1/2 turn using a standard screwdriver to access the oil drain plug. It’s been on there for 21+ years. I even sandwich it between the floor jack and the crossmember when I lift the vehicle and it just shrugs it off and keeps on shielding.

I cannot attest to any mileage gains by it being there. The Envoy used to get 16-18 mpg when we got it 12 years ago. Now with General Grabber tires (better snow traction than the crappy Continentals that were on it) it gets 10-12 mpg for a range of less than 200 miles per tank.

Amy Andersen
Amy Andersen
4 months ago

My Envoy was missing the part that comes off for oil changes, presumably because some quick lube shop removed it long before I got the car and never reinstalled it. I can attest to the sturdiness, though (and the terrible fuel economy; there’s a reason I got rid of the damn thing)

Mrbrown89
Mrbrown89
4 months ago

And for some reason its always a recent Ford vehicle dragging/flapping their shield plate, even F150 trucks. One oil change and they don’t fit properly anymore. My GM cars are being pretty reliable on this aspect.

Geoff Buchholz
Geoff Buchholz
4 months ago
Reply to  Mrbrown89

YES. A couple of years ago, my now-husband and I were driving back into the city on the Eisenhower Expressway after Thanksgiving in his Escape when we suddenly heard the God-awful dragging of the plastic underbody shield … and thought we’d had a blowout. A poorly-tied shoelace secured it until we could get it to a shop.

Cerberus
Cerberus
4 months ago
Reply to  Mrbrown89

Besides driving incidents, I think it’s mostly down to lazy/incompetent oil techs and that’s why I change my own oil (had two Fords that never dropped the covers and I’ve seen plenty dragging with drivers that do not look like they change their own oil). Just the same, they could be better secured or made of more durable material.

Captain Muppet
Captain Muppet
4 months ago

I’ve been in OEM meetings about these things, and they are needed.

Sure, a tiny increase in mpg won’t bother you, but a tiny increase in mpg for tens of millions of cars has a big impact. It’s not just aero drag either, it’s reducing lift (and reducing drag, that’s the stuff aerodynamicists dream off). Do you notice less stability at very high speeds? Probably not, but we have to engineer cars to be safe at any speed. There was a book about it.

They cut down on noise emissions too, which you won’t notice inside your car, but you will notice if you’re trying to pass a homologation pass-by test and you’re a decibel over the limit. Making the car quieter means we can use some of those decibels for louder exhausts, intakes and tyres. These are fun things.

Then there’s the cooling effect. Once air has passed through your radiators it’s job isn’t done. Loads of work is done using relatively small features to guide cooling air to turbos, alternators, any sensitive electronics, and if the air can all just get dumped out through a hole in the floor all that work goes to waste. You won’t notice, because you aren’t vmaxing your car, or towing a trailer up a mountain, but without significant issues in testing we wouldn’t be fitting them in the first place. You want more melted alternators on 20 year old cars? That’s how you get them.

Yes, missing access holes for servicing are an unforgivable error, and sure, the fasteners are cheap and light. But do you all want to pay more to replace all your fasteners with something robust? The people who buy new cars do not.

Underfloor shields benefit everyone, but in ways that are significant on a vehicle fleet level, rather than individually.

Gabriel Jones
Gabriel Jones
4 months ago
Reply to  Captain Muppet

Call a meeting right now and replace the sloppy push to fit plastic fasteners with some metal quarter turn fasteners like this used on removable panels in the aviation world.

Captain Muppet
Captain Muppet
4 months ago
Reply to  Gabriel Jones

I get called in to meetings, I don’t get to call them. But sure, add £30 to every one of tens of millions of cars every year for the benefit of the third owner in eight years time. If we can’t justify zinc plated panel nuts and screws we certainly can’t justify aerospace fasteners.

You know what we should do? Design them all to be cable-tied on. It’s how we’ll fix them on eventually, why not lean in to the cheapest, lightest robust solution? Because (and I know because I keep suggesting it) it doesn’t seem professional.

I held the entire front bodywork on to my Elise with cable ties. For 9 years and lots of high speeds and track time. Loads of clamp load available, unlike plastic push fit fasteners. You can even get reusable cable ties so it’s environmentally friendly. I’m still trying to get through a bag of 100 I bought ten years ago, but I keep reusing them.

Santiago Iglesias
Santiago Iglesias
4 months ago
Reply to  Captain Muppet

That would never fly though, would be way too much operator time at the factory

Captain Muppet
Captain Muppet
4 months ago

Yeah, that’s really for the niche boutique manufacturer I wish I worked for.

Spikedlemon
Spikedlemon
4 months ago
Reply to  Gabriel Jones

My Honda Civic has exactly that holding on its metal under-engine shield. Metal quarter-turn fasteners with large flanges built into them.

But sadly the metal shield is very closely related to tinfoil, and the first winter’s snow/ice heavily dented it from crap dropped from cars ahead. So it’s been replaced with a more robust plate.

Funny to think of a Civic with a skidplate, but here I am.

Bite Me
Bite Me
4 months ago
Reply to  Captain Muppet

Ah yes I love the high speeds and loud exhaust of the Fit I just ripped the underbody panel off of

EXL500
EXL500
4 months ago
Reply to  Bite Me

I thought it was just our Fits that had this issue. I’ve had to replace fasteners multiple times over the years. God forbid you go through even moderately deep water.

Bite Me
Bite Me
4 months ago
Reply to  EXL500

I’d taken it in to get at least zip tied back into place 3 times before I just got under it with a knife and took the damn thing off.

Captain Muppet
Captain Muppet
4 months ago
Reply to  Bite Me

Maybe your Fit has low gearing to make it possible to get adequate performance from revving the crap out of it, if so they may well have had to use higher gearing to get through the pass-by test with extra underbody wind noise. That would have made it slower and less fun.

OEMs hate spending money, they wouldn’t fit flimsy undertrays with fragile fasteners if it wasn’t of measurable corporate benefit.

Parsko
Parsko
4 months ago
Reply to  Captain Muppet

DAD, leave me alone!

LALALALALALALALALA!

Brynjaminjones
Brynjaminjones
4 months ago

I see these flapping violently very frequently here in the UK, and it’s almost always a VW.

Rockfish
Rockfish
4 months ago

Um, those panels have a primary purpose of helping the engine warm up to a temperature where it’s most efficient. Then it’s kept there by the thermostat, etc.

Especially important for something like a turbo diesel.

Plus, some have NACA vents for positive pressure cooling in just the right places.

LMCorvairFan
LMCorvairFan
4 months ago

Agree 100000%. Had to R&R several to change engine and cvt oils and coolant as well as fix a heat shield that had torn loose from its fasteners. The fasteners on most of the plastic panels had failed as well as many of the stamped clips. The dealer fixed or replaced all of these when i had the car in for recall work. They didn’t charge a dime and had a bit of a laugh with me about the creative zip tie work i did. The dealer is astoundingly great.

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