Plastic underbody panels on cars... What are they good for?

[Brendan W]

What they say.....
Fuel economy
Reduced kerbside noise especially diesels
More difficult for road debris to take out aux belt and timing belt

They obviously catch tools when you drop them and can hide a fluid leak for longer that you might want.
Eventually I fail to replace it on any car I have owned. More trouble than they are worth imho.

[Vmass]

A couple years ago I was out in the middle of nowhere in South Carolina and all of a sudden had this extremely loud noise and vibration. I thought the transmission had fallen out.

Turns out it was one of those panels, very large one. Had to rig it up somehow as a few clips were missing. I assume mechanics love them because it helps keep the engine and bolts free from corrosion.

[Baatfam]

They obviously catch tools when you drop them and can hide a fluid leak for longer that you might want.
Eventually I fail to replace it on any car I have owned. More trouble than they are worth imho.

Yah, the tool/part thing is a risk.
But if the car is designed right, you should never have to mess with it, unless your doing something major.
I've taken mine off once in two years of ownership, because I upgraded the intercooler.

[Jedz123]

What they say.....
Fuel economy
Reduced kerbside noise especially diesels
More difficult for road debris to take out aux belt and timing belt

They obviously catch tools when you drop them and can hide a fluid leak for longer that you might want.
Eventually I fail to replace it on any car I have owned. More trouble than they are worth imho.

Yes the draw back with reduced plastic panels is increased cabin noise, I'll admittedly second that. Glad I'm not the only one that sees them as trouble.

[Jedz123]

Yah, the tool/part thing is a risk.
But if the car is designed right, you should never have to mess with it, unless your doing something major.
I've taken mine off once in two years of ownership, because I upgraded the intercooler.

I find it Funny that your Fiat is better designed under the belly than my Honda. I just talked to my boss about this (he has a Honda CRV) and has issues with them as well, both of use had to remove the bottom pan under the engine in order to perform an oil and filter swap. We both also have pitched ours right from the start because they ultimately fell out on use while driving in the snow.
Truly glad you don't have issues.

[Baatfam]

I find it Funny that your Fiat is better designed under the belly than my Honda. I just talked to my boss about this (he has a Honda CRV) and has issues with them as well, both of use had to remove the bottom pan under the engine in order to perform an oil and filter swap. We both also have pitched ours right from the start because they ultimately fell out on use while driving in the snow.
Truly glad you don't have issues.

Well, like I said, no snow for this car. But I lived most of my life in the north, and a couple cars with belly pans. Don't know.

As for oil and filter. The filter goes in from the top, and I use an oil extractor to remove the old stuff. Don't even jack it up.
I use the extractor on all our cars now. The other two I can reach the filter without jacking them up.

[LAB3]

More difficult for road debris to take out aux belt and timing belt

Had an 87 Dodge I bought in Santa Fe with a go-fast engine, the timing belt cover was left off to save weight. Sure enough, after a couple of months in the Michigan winter it jumped timing due to snow/ice build up.

Over the years I've had plenty of vehicles that have gotten hung up in deep snow and can'y say that a belly pan would have made much of a difference. Knowing me if my car had one, it would be left off in favor of convenience in servicing it in the future, then something like that would happen. One of the things I've learned from wrenching and having lots of family in the auto industry, a manufacturer isn't going to put the resources into making a part and putting it on without a good reason.

[bwringer]

On many new cars in the last year or two, "fuzzy" underbody pans have started to appear, apparently for noise reduction. An absolutely abysmal idea for cars that are ever driven in rain, on dirty roads, in cold weather, etc. One of the more absolutely stupid and utterly doomed things I've seen in a while.

Obviously, you need things like fender liners and panels under the engine to keep spray off the belts, alternator, and suchlike. Some have useful hatches or openings to allow maintenance, but far too many require you to remove a dozen or more heavily corroded bolts just to do an oil change. If you take your car to a quickie-lube joint (horrors!), don't be shocked to find someone has hacked a hole into the belly pan, discarded the whole thing, or left out or stripped most of the bolts.

[rphillips]

Reading all this & remembering back when there was almost "NO" plastic on an auto. inside or out, especially underneath...Back then at 100K it was time for an eng. overhaul, now just broke in good...Man how things have changed.

[Brendan W]

A couple years ago I was out in the middle of nowhere in South Carolina and all of a sudden had this extremely loud noise and vibration. I thought the transmission had fallen out.

Turns out it was one of those panels, very large one. Had to rig it up somehow as a few clips were missing. I assume mechanics love them because it helps keep the engine and bolts free from corrosion.

For some reason, many constructors manage to use three different types of fastener on them and inevitably grease monkeys get lazy or confused and by the second or third oil change the panel is a mish-mash of self tappers and other various bodges. I'm not surprised to see so many flapping about, drivers oblivious for the most part.

Yah, the tool/part thing is a risk.
But if the car is designed right, you should never have to mess with it, unless your doing something major.
I've taken mine off once in two years of ownership, because I upgraded the intercooler.

You sound like our Citroen dealer. No tool kit? Why it's so reliable you'll never need it and so complicated it would be of no use anyway

Yes the draw back with reduced plastic panels is increased cabin noise, I'll admittedly second that. Glad I'm not the only one that sees them as trouble.

One of the things I've learned from wrenching and having lots of family in the auto industry, a manufacturer isn't going to put the resources into making a part and putting it on without a good reason.

You know those sites that tell you, in semi-conspiratorial tones, the real reason for such and such.....
Well some of them claim that the undertray primary function is to reduce noise, not in the cabin, but the noise as perceived by a pedestrian as required by EU regulations?

[dpep]

So noise reduction or streamlining? Does anyone know if they are present on electric cars?
...

[Jedz123]

So noise reduction or streamlining? Does anyone know if they are present on electric cars?
...

That's a great question! I know in Tesla the "belly" is mainly comprised of the storage area for the battery so my bet is it's made of a stronger plastic or some form of steel...

[Jedz123]

And for your viewing pleasure...


Looks like the plastic panel snapped, must have been on that -23' F morning on my ride to work last week...All plastic is brittle at those temps. Can't imagine how else it broke... Must have got snagged on snow when we got 4" yesterday on my way to work (roads were not plowed on my commute).
Now that the pavement is clear of snow and ice It's in essence the card in the spokes but far more annoying and obnoxious.
Smack dab in the middle of the car.

[Jethro]

The car does have a plastic valve cover but I think that's it. Very much a Honda in the build quality around the engine and transmission.
Your the only one on the forum that has seen the mini beast tow with both of us in it...
Your truck is bad a$$ though...

That's right, one fat man and one corn fed VT farmboy pulling a loaded trailer with a Honda Fit in 40mph crosswinds- And getting 27mpg while doing it! Pretty awesome.

[dorkburger]

Our Hoda Pilot has a full plastic rear bumper cover. This summer I noticed that the steel structure behind the plastic that is at least 25% gone from rot. I can only assume from the cover holding in snow / slush and the salt that comes with it. Around here they salt and brine to the point that when everything dries there is salt dust flying in the air on highways.