do plastic skid-plates on cars actually do anything?

September 22, 2006 1:51 PM

the plastic netherparts under the engine of my jetta have finally fallen out, after some altercations with those concrete front-tire stops in parking lots. is it important for the future of the engine/mechanical bits to get these replaced?

it seems like a rather expensive replacement, which is quite possibly just cosmetic. i don't intend to sell the car, so cosmetics don't concern me.

to better describe the parts now missing--these are not the "ground effects" directly beneath the bumper. nor are they the plastic bits that separate the wheelwell from the engine compartment. rather, they are a couple of black plastic plates that were directly under the engine, probably where a "skid plate" would be if this were a truck.

posted by garfy3 to Technology (12 answers total)

I had the same thing on my old Audi - I used to take it off every couple months to change the oil and finally got sick of it - I had it off for about 2 years until I finally traded it in for a new car last month.
posted by quadrinary at 1:54 PM on September 22, 2006

(by which I mean nothing happened - I think it's just to keep the engine and belts clean, in all honesty)
posted by quadrinary at 1:55 PM on September 22, 2006

I suspect that their only purpose in life is to keep the engine clean. However, if you're riding through slush or dirty water, you're going to wind up with all sorts of grit and grime getting up into the engine compartment. It likely won't do anything but wear out belts a little faster... but, it could exacerbate future problems.

But, it's a Jetta. I think you'll probably be fine.
posted by Netzapper at 2:06 PM on September 22, 2006

They're called skid plates on VWs, too. The plastic one on our nubug got ripped to shreds in the first few years of its life (due to some gravel-road incidents.) They protect the oilpan, among other things, so it's a good idea to have something there... we opted to replace the plastic one rather than fork over several hundred for an aluminum one.
posted by runehog at 4:25 PM on September 22, 2006

Depends on a lot on where you live.
If you live somewhere where they salt the roads on a regular basis, they have a large protective benefit.
If you live in Southern California, not so much.

Are you somewhere where the roads are often covered in loose gravel or rocks (from repaving or otherwise)? Better to have the cheap plastic taking those shots than the expensive oil pan.

Also, they do (to a small degree) aid with aerodynamics, so you may notice a .25 mpg drop with them gone.
posted by madajb at 5:11 PM on September 22, 2006

When they came partially loose on our car, I mentioned it to the mechanic. He said they'd just take them off and throw them away (and charge for a half-hour of labour) and that I could just pull them off myself.
posted by winston at 5:50 PM on September 22, 2006

Had something similar on my 2001 Passat wagon. Talked to a mechanic who has worked exclusively on VW's for years, and he told me to throw it away. He said the shield was supposed to aid in diverting air around engine for cooling purpose but in his experience had no effect on engine temperature and performance, and that removing the shield would actually improve my gas mileage by a couple of mpg. He was exactly right - no effect on temperature, and mileage improved immediately from 28 to 30 mpg.
posted by Jackson at 6:43 PM on September 22, 2006

I have an aluminimum skid plate from dieselgeek on my mk4 jetta. Now I don't cringe whilst driving in the city. I reccomend it.
posted by funkbrain at 6:48 PM on September 22, 2006

The underbody trim also serves to smooth the airflow under the car, and thus theoretically keep the car stable and attached to the road at high speeds. High speeds, like 100+ MPH. I also have an Audi like quadrinary :)
posted by intermod at 8:14 PM on September 22, 2006

Response by poster: hrrm...i'm in the northeast US, so there's certainly some salt on the roads in mid-winter. and i plan on keeping the machine till it literally falls apart, so based on what runehog and madajb imply, it's probably something to take care of before the roads get icy.

that said--anybody have experience with how much it costs to put new ones on? i imagine a body shop could do it, but they'd probably charge a ton in labor...
posted by garfy3 at 7:35 AM on September 23, 2006

The underbody shields often are an important part of the airflow through the engine, in particular, through the radiator of the engine. If losing them means a higher pressure area forms behind the radiator, you lose cooling, which can be a real problem. It may not affect you, but it might. If you have a real temp gauge, and you've been watching it, you can see the difference, if there is one.

Overheating is the single most common reason engines fail.
posted by eriko at 8:31 AM on September 23, 2006

Mine fell off as well due to excessive curb checks. The only issue I've had is when it rains, water affects my power steering belt or something making it difficult (but not impossible) to turn the wheel.
posted by slim at 9:29 AM on September 23, 2006