Missing Underbody Plugs

Looking around under my Golf I noticed four open holes, two each side behind the rocker panels. Above these holes there’s a large enclosed space. Lots of potential for car-killing corrosion here if you’re in the rust belt.





I found three of the four missing plugs inside the body. The plugs had a thin external flange that had dried out and cracked off, with the plugs then escaping inside the body.

Here’s the part number for the replacement plugs: 1K0899185. This is an upgraded part that looks like it will be more durable than the original plug – 30 cents each from 1stvwparts.

I might be mistaken, but i believe these are the holes used when they put the car on the lift mandrels. Might be why you found the plugs inside. Thanks for the part number!!! Im missing 2 on the Jetta one on the Passat

There *might* be some holes that are in a reinforced area and which are plugged by these parts or can have the lift pads installed in them. However, not all of the areas plugged by these parts would be suitable for lifting. I think the main reason for the holes is to drain the car body when it is submerged in liquid during the cleaning and prep for painting.

These plugs of course need to be there and they should also be covered over with a layer of undercoating spray. For additional protection you could spray rust inhibiting material inside some areas although not everywhere. For example, one pair of these plugs is topped by the carpet pad and carpet in the rear seat floor. I know this because I repaired my floor pan earlier this year after we drove over some metal that banged up that area.

I used "Fluid Film" to spray in some other areas such as inside the doors. I know it sounds radical but this product is quite thin and doesn't stink like oil.. I think it might be lanolin wax based. I got mine at a John Deere dealer but you can also get it from McMaster-Carr.

There are some small body holes that should not be plugged. These have rubber plugs in them that are about 20mm across and have holes in them about 5mm diameter.... actually I guess I don't know why you cannot close them but from the design it seems pretty clear they are supposed to be a drain. These seemed to be in all the areas where the sheet metal formed a box section under the car.

wncav8er said:

I might be mistaken, but i believe these are the holes used when they put the car on the lift mandrels. Might be why you found the plugs inside. Thanks for the part number!!! Im missing 2 on the Jetta one on the Passat

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I'm pretty sure these holes are not used for lifting or tying down. As mk3 said, they look like drain holes, maybe for the waxy coating that VW uses for rustproofing.

The thin external flange had cracked completely off the old plugs - a design defect of sorts, I suppose. Not a big deal in the South, but up here in the Northeast road salt will enter through those holes and get to work on all the crevices in the space behind the rocker panels.

mk3 said:

I used "Fluid Film" to spray in some other areas such as inside the doors. I know it sounds radical but this product is quite thin and doesn't stink like oil.. I think it might be lanolin wax based. I got mine at a John Deere dealer but you can also get it from McMaster-Carr.

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Not radical at all -
I spray down the underside of all my vehicles with Fluid Film every fall, plus use it for many other things.

I discovered these holes on my Jetta a few years back and I ordered two replacement plug types and both were wrong. I got some type of drain hole seals. My local VW dealer was clueless. I located a TSB that described what these holes are for. They are to install the vehicle restraints when the cars are shipped via boat. The dealer at dealer prep is supposed to plug these holes. Maybe they did, but the plugs fell out.

Thanks for the part number I'll have to see if they fit the Jetta. Mine appear to be a different shape. This is a picture of the fronts on mine. The rear holes are a different shape yet.



I ended up taking a thick plastic sheet and cutting out pieces a little bigger than the hole and smearing roofing dry/wet patch (asphalt) over the holes with the plastic between the tar and holes in my Jetta.

dadsdiesel said:

Not radical at all -
I spray down the underside of all my vehicles with Fluid Film every fall, plus use it for many other things.

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What do you guys use to spray it? I bought a couple gallons and the sprayer they recommended on their site a few years ago:
http://www.theruststore.com/Undercoating-Gun-System-for-Fluid-Film-P216C67.aspx?UserID=7205765&SessionID=KSDxJVNp{nfeb4zfx299

And I don't like how thick it goes on. I spray it in the fall, but I'm not convinced its still there even halfway through the winter.

I like this product more, because it dries and forms this tough barrier that fluid film doesn't seem to have.

http://www.lpslabs.com/product_pg/corrosion_pg/LPS3.html

PDJetta said:

I discovered these holes on my Jetta a few years back and I ordered two replacement plug types and both were wrong. I got some type of drain hole seals. My local VW dealer was clueless. I located a TSB that described what these holes are for. They are to install the vehicle restraints when the cars are shipped via boat. The dealer at dealer prep is supposed to plug these holes. Maybe they did, but the plugs fell out.

Thanks for the part number I'll have to see if they fit the Jetta. Mine appear to be a different shape. This is a picture of the fronts on mine. The rear holes are a different shape yet.

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I can't be sure that my 2003 Golf has the same holes in the underbody as your 2004 Jetta.

Having said that, after discovering these unplugged holes I went to town on the subject of underbody plugs. The open oval holes in your picture are the tie-down attachment points referred to by the TSB. If you want to plug these holes, the plug part number is N90402801, though this plug is poorly designed and I found it necessary to trim the external flange slightly to make them fit. The circular plug in your picture is part number N10138801.

Here's my (somewhat) complete list of MK4 underbody plugs:
1K0899185 40mm round plastic plug for flat hole -- two on each side behind rocker panels
N10138801 30mm round plastic plug for deep hole -- one on each side behind front wheels
N10226501 30mm round plastic plug for flat hole -- one on each side in box section
N90508801 44x24mm oval plastic plug for flat hole -- four in each rocker panel plus one more each side
N90402801 30x14mm oval plastic plug for deep hole -- one each side behind front wheels
Unknown part number 19.5mm round plastic plug for deep hole -- one each side in front of rear wheels

Yeah...I wasn't sure if these were the holes for the lift or just the underbody drains. The ones for the drainage/ETC do usually have the rubberized coating (that doesnt stick well to rubber) on them.

I love fluid film and LPS3. I have gallons of both next to me as I type this. You almost might try ACF-50. It is a great anti-corrosive but a little pricey. We use it on all of our Helicopters here in the Gulf of Mexico.

I bought Fluid Film in a spray can so I just put the little red straw in all of the drain holes in the door and shot the film as horizontally as I could. I did the same thing in the closed box sections of the underbody by sticking the straw through the 5mm hole in the smaller rubber plugs.

I also sprayed Fluid Film on some external parts of the underbody in the region of the muffler but this was only as a test - I think the product will not last very long there.

I plan to research LPS 3 and ACF-50 - sounds interesting.

I also re-sprayed the entire underbody (going over the top of those big plugs) with 3M 08883 after I repaired a few tiny areas of rust and after repairing the damage from the metal the car ran over. I'll probably re-check the underbody every year before winter.

I realize that Fluid Film isn't the best rust inhibitor for under our vehicles, but since I always have some around, I feel it doesn't hurt to spray the undercarriage once a year.
Where I live they use a 50/50 mix of salt & sand in the winter that sticks like glue to everything. I feel that at least a light coating of Fluid Film helps a little.

I also use it on my lug bolts/nuts when changing wheels, the mechanical parts of my trailer hitch, lubricant for my barn door rollers, etc. etc.

I just use the spray cans - buy it by the case.

Fluid film or Wurth body protection wax sprays are meant for body cavities and need to be replenished every few yrs because they melt and run off in summer. But as a moisture barrier are the best...kept the rust of my scirocco for 20 yrs

For a "Total Package" under-carrage rust preventative this is about the best you can use. If you live in the rust-belt (anywhere they use road salt) this product is the solution.
http://mil-specproducts.com/productPage.aspx?prodID=355

A gallon will cover nearly a 1,000 Sq Ft. A quart would do about 250 Sq.Ft which is more than enough to give your A-4 a 1MM thick film of long term protection/

TECTYL 846, CLASS I
MIL-PRF-16173E, Grade 4 Class 1 Corrosion Preventive Compound Tectyl 846 (Grade 4, Class 1) is a modern version of the World War II cosmoline type corrosion preventative. Technically, it is a solvent cutback, water-displacing corrosion preventative compound that leaves a coating that can be described as amber in color, translucent, waxy and "non-tacky". Tectyl 846 is available in aerosol cans exclusively through F&L Petroleum Products. Tectyl 846 is a Qualified Products List (QPL) product. While many commercial industries use Tectyl 846 for it's superior, long-lasting preservative capabilities, it is also the most common preservative used by the United States Military to protect their equipment. It can be applied easily by spray, dip, or brush and will provide years of protection in both indoor and outdoor environments. For more information, please click on the "Tech Data Sheet" link below. Qualifications/Specifications Met: MIL-PRF-16173E, G4 C1 | MIL-P-116J, Type P-19 MSDS Tech Data Sheet Got a question? Ask our expert E-mail a Friend Catalog Pricing - Order Product Here

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migbro said:

Here’s the part number for the replacement plugs: 1K0899185. This is an upgraded part that looks like it will be more durable than the original plug – 30 cents each from 1stvwparts.

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What did that site charge for shipping? They say they calculate at the time of shipping?

theantirice said:

What did that site charge for shipping? They say they calculate at the time of shipping?

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They charge whatever it costs to ship the parts that you order.

actually, 1stvwparts.com has an $8.95 minimum for shipping.

migbro said:

Here's my (somewhat) complete list of MK4 underbody plugs:
1K0899185 40mm round plastic plug for flat hole -- two on each side behind rocker panels
N10138801 30mm round plastic plug for deep hole -- one on each side behind front wheels
N10226501 30mm round plastic plug for flat hole -- one on each side in box section
N90508801 44x24mm oval plastic plug for flat hole -- four in each rocker panel plus one more each side
N90402801 30x14mm oval plastic plug for deep hole -- one each side behind front wheels
Unknown part number 19.5mm round plastic plug for deep hole -- one each side in front of rear wheels

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All first 5 part #'s are correct, but the last one is giving me a problem.
Does anyone have the part number for the last one?

migbro said:

Unknown part number 19.5mm round plastic plug for deep hole -- one each side in front of rear wheels

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I have removed all 4, but there is no part # on them.
Help!! Mine are old and cracked. Have 03 Jetta Wagon.
All the websites with parts diagrams are no help.

crawdaddy said:

All first 5 part #'s are correct, but the last one is giving me a problem.
Does anyone have the part number for the last one?

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ECS has them: here

mjydrafter said:

ECS has them: here

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I think he means this one...20mm round....
https://www.ecstuning.com/b-genuine-volkswagen-audi-parts/body-plug-20mm/n10124501/

All....
https://www.ecstuning.com/b-genuine-volkswagen-audi-parts/c-exterior-body-sealing_plug/

maxmoo said:

I think he means this one...20mm round....
https://www.ecstuning.com/b-genuine-volkswagen-audi-parts/c-exterior-body-sealing_plug/

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Yes, I did mean the round deep 20mm bung.
The second link, are they all for the mk4?

My suggestion is to go to an auto wrecker and get the plugs there!
Of course this is an ancient thread and the OP probably doesn't even have the car anymore.

Jetta_Pilot said:

My suggestion is to go to an auto wrecker and get the plugs there!

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I was also thinking of doing that, but they will be same condition as my old ones.

I got them from idparts. It’s not hard to spend 50 if you get some of each kind with extras. Ecs gives free shipping at 50 which isn’t hard to blow if you get some of each type of plug. The ones posted from ecs are all on a mk4, although I’m not sure about the strut towers. Mine were mostly cracked or missing, I still have some cracked hot wax oval ones I’m hesitant to mess with. I’m also wondering which ones are drains.. junkyard plugs is what I tried first and they are garbage by now