Main.TrailIndexPage | Chassis and Body | Water Drains

Water drains

This component is part of Chassis and Body. The body has a number of water drains that aid in getting rid of water from the body of the car. If these drains are clogged, this may lead to rust forming. They can be clogged due to leaves, dirt, rust, and indeed deterioration of rubber hoses in certain parts.

The following drains are identified:

Symptoms of trouble

If you have a wet front carpets after driving in the rain, then it is possible that your heater drain tubes are clogged. Check the section below on un-clogging the heater drain.

There are other sources for wet floors: windshield wiper arm gaskets, soft/hard top and side glass gaskets, wiper motor chamber drain holes, and not to be forgotten is dried out windshield rubber gaskets, leaking around the glass, a common occurence in older benzes which can lead to rotted floors, as the water sits undetected under the mats. These windshield rubber/gaskets should be renewed probably every 10 years. If you are not sure, check them next time it rains.

Soft-top Compartment Drain

In the soft top well are two drains at the front where the top bolts down. These are actually rubber tubes and they can easily become plugged.

If your top rubs against the seal it will slowly wear it away leaving a spot for water to enter. The channel that holds this seal often rusts away and this also allows water to get in. The seal itself has a drain where the channel in the rubber starts. There's a small hole and the water drains through it and hits a baffle on top of the wheel house and then exits just above the rocker cover between the door and wheel opening.

There are two drain holes at that area and they too can get plugged. A good shot of air will usually open it back up. Water in and of itself is no so bad. It's when it lays in one place for a long time on a continuous basis that you will have problems.


Drain through B-pillar



Drain tube in soft-top compartment



Drain in B-pillar


Heater Drain (or Ventilation Drain)

The Pagoda has drain hoses at the heater or ventilation air intake box (scuttle box). Just to make sure we are clear on this, I'm referring to the air scoop under the windshield. Water and dirt get in through the opening and drain out through two rubber ball like fittings on the engine side of the firewall. One is located near the exhaust headpipe, the other is below the brake booster/master cylinder.

The cowl vent drain hoses are short 5-6" long rubber hoses (3/8" diameter) that are visible underneath the dashboard on the sides of the heater matrix box which is fastened to the firewall. If you look very deep underneath you will see the metal painted (body color) elbows for the drain pipes coming from the top and facing the front of the car. There is the rubber hose and then it connects to another metal body colored pipe which goes straight through the firewall into the engine compartment. If you look under the hood in the engine compartment area near the gas pedal linkage running along the firewall you will see two pipes sticking out. The ends of these pipes should have a funny black rubber boot at the ends that look like crab claws, these are the outlets of the drains.

The easiest way to locate the drain hoses is to start at the point that the metal tubes protrude through the front of the firewall. Once you get yourself oriented, then look up and under the dash at the point you saw the tubes on the other side. They are clearly visible and replaceable without needing to take anything else apart.

Squeezing the rubber balls and tubes may help in determining if the drains are blocked. Additionally you may run a small wire up the tube to make sure.

Don't use a coat hanger to try to unplug the drains... the drain tubes are rubber when they cross the foot area. If they have never been replaced the wire will tear them. If the rubber is in that bad a condition it definitely needs to be replaced. It is just rubber hose with a couple of hose clamps. Not very hard to do.

The rubber hose is a standard rubber hose that can be bought at an auto store.

These will allow the free flow of water but can become plugged with tree needles, leaves, etc. When this occurs water can become trapped in the tubes, backing up and into the interior of the car. If the connecting rubber hoses are in good shape (found under the dash above the footwells) leaks may not show up. Water will be accumulating where it should not be. After a time the metal tubes may rust through and then the water can build up in the firewall crossmember channels.

These channels can hold considerable amounts of water (several litres) as they are continuous from side to side. You don't want this to happen. Your car is now rusting from the inside out and you won't know for some time.

Cleanup Procedure

The following procedure is recommended for W113 Pagoda owners experiencing water leaks in the interior of the car under the dash. Water entering the car during or after a rain storm are usually related to problems with the "fresh air" vent located forward of the windshield. If this problem is left unattended it will not only ruin the carpet, but cause rust deterioration of the floor itself.

The fresh air vent should be examined for debris, clogged drains, cracks in the drain hoses, and deterioration of the original water sealant applied by the factory. This is not a difficult job for the DIYer. A complete check is as follows:

  • Raise the hood and remove the three screws fastening the chrome front piece of the vent.
  • Remove the two lower screws of the cowl and the two screws located near the windshield wipers.
  • Loosen the four screws located inside the cowl along the rear. The cowl will now lift off. Detach the windshield washer hose from the spray nozzle.

Showing the scoop removed


  • Open the vent half way via the interior dash control.
  • Remove the four 10mm bolts (don't worry, the nuts are fastened to the underside).

Removal of air intake


  • Lift up the swivel cover and push out the cable rod.
  • Remove the cover.
  • Remove the filter by, first, gently lifting one of the top corners to locate the wide "spring" on the underside of the filter. The spring is held in place by three small brackets forward and back of the filter.

Carefully unplugging the drain tube


  • To remove the filter, gently compress the spring along the 3 upper brackets to release it. Use care not to damage the filter or spill excess debris into the vent area. (The filter can be vacuumed or gently washed prior to reinstallation).
  • Use a shop-vac to remove any debris from inside the vent area. Use a screw driver or other tool to prise up any factory sealant that has loosened. (The factory sealant resembles caulking compound in appearance).

Pay particular attention to the sides near the drain holes, checking for any cracks in the sealant along the sidewall seams. Scrape loose debris and remove. Ensure that both drain holes are clear of debris. (If water does not drain properly through the drain holes, it will spill over the walls of the vent compartment and into the interior vents or blower.)

Clean the vent compartment thoroughly with shop-vac and rags. If rust is present, use Permatex Rust Eliminator or other such product to neutralize any rust. Apply a high quality automotive silicone (3M or other brand) to seal the entire area, paying attention to the metal seams on either side of the inner vent area.

Many leak problems are associated with loose sealant in the seams of the side walls of the inner vent. When the sealant looses its effectiveness, water can pass freely to the interior side vents, even when the drain holes are clear Reinstall the filter, swivel cover, cowl and chrome in the reverse procedure of the above. In the interior of the car, remove the lower under dash panel above your feet (if present in your car).

Check the drain hoses. These are 6 inch hoses running from the vent box above and outwards to a metal tube in the firewall. Remove the lower clamps and check for debris. If hoses are dry or cracked, replace with similar hose from your local hardware store. (Clear hose works well so that you can examine for future debris without removal). Finally, check the "bubble" drain hose located at the firewall in the engine compartment to be free of debris. No more wet carpet. No more wet feet.

On a right-hand-side drive the brake booster, steering box, and exhaust make access to the firewall side of the drain tube quite difficult.

Heaterflap leaks

If you still have a water leak after fixing the drains, Tom Sargeant learned that if his air scoop was open (top left lever to the far left blue arrow) and his heater was closed (bottom left lever to the far right), water can come in to the car under the dash. That is because the flap that closes the heater box opens the air flow into the car-similarly, when the heater box flap is open, the air ducts into the car are closed.

Worse scenario for rain is a closed heater flap and open air scoop, as rain can come in through the air vent. If you remove the cowl chrome and cowl, all of the mechanical flaps are exposed and you can see how this all works. All of this assumes the flaps open and close based on the length of the cables. I discovered mine did not and had to add to the length of the cable.

Another possible entry point is on the sides of each of the walls of the intake scoop. They are not as high as I think they could be and some water could rush through there and get into the car. I could not get to the hose under the dash on the passenger side due to the A/C. What I did was take a 1/2 inch clear hose (Home Depot), cut it to create a sharp point, sprayed it with silicone to make it easier to insert and fished it through from the air intake drain through the old hose and out the passenger side exit in the engine area. This is essentially a sleeve. I then caulked around the drain in the air intake area.

Achim writes: the lower heater flaps (which go for left and right side) are prone to problems, especially the left one. Take them carefully out, clean everything thoroughly, reglue them with epoxy (if necessary) and especially put a few drops of oil to the linkage rod of the heater valve and the hinges of these flaps. That will help your heater levers in the dash a lot.

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I want to remove my air Intake Cowl so that I can sleeve the tubing with plastic tube and check my filter and clean everything out. Inside in the back of the cowl are 3 or 4 screws. My Question is about those Screws ... Do I have to remove the screws completely or just loosen them? They are in a very awkward place. Is the cowl slotted OR drilled?

You need only to loosen those screws as the cowl will lift straight up, after the chrome grille and the teo screws in front and the two near the wiper arm connectors(these might be buried under paint and debris).

Who here knows how to remove the butterfly flapper valve from the chrome fresh air vents on the left and right side of the dash? I had no difficulty in removing the vents, but have no been able to figure out how to remove the post that goes through the center of the butterfly valve so it can be removed. Has anyone had any experience in removing this?

Bob Smith: I had my air scoop off today with the intention of cleaning out the well and filter etc. How do you remove the hinged air flap inside the scoop? I thought I would remove the bolts to the hinge but the nuts are on the inside of the flap and are not accessible. Just right for never getting back on! OR are the nuts welded to the inside of the flap? I looked at the hinges and they seem to be nylon once only fittings.

I just dismantled my heater and - unfortunately - you'll have to remove the defroster ducts to get to the bolts that hold the flaps. I can't imagine why the car was built this way, but it was (perhaps Mercedes has a special department called Difficulty Engineering). Just to warn you, removing the duct from the driver's side, will require removal of the windshield wiper linkage - not fun. There is also a center mounting bolt for the blower cage the nut for which can only be accessed by removing the plate on the right side of the transmission hump. If anyone out there knows of an easier way, please speak up; I've still got to put everything back together.

Bernt Damm says: which flap is Bob talking about? The fresh air flap is removed by undoing the left side 2 bolts on top of it and then sliding it out sideways. As for the inside 2 black flaps that control the heater, you need to unscrew them from inside the car. I did this without undoing anything in the car but you need to be flexible and you need a 10 mm mini socket set with 1/4" drive. It is the bolt on the driver side that is really difficult to get to. and yes, the nuts are welded to the the flap fittings. Then again Bob has a right hand drive so it is all completely different again. It may be a lot easier ot more difficult to get to the 2 bolts. I had to take them out because the flaps were broken off but I would certainly not ever do this just for cleaning...

Bob replies: Bernt, The flap (vent cover) I am talking about is the main one that shuts and keeps the air out of the car. There are four bolts (2 on each end) that need to be removed BUT the nuts are on the inside of the flap and look prone to dropping into the space below. The flap on my car does not open to a vertical position only about 45 degrees, hence my difficulty in removing the bolts and nuts. I was wondering if they are welded onto the underside of that flap? I don't want to drop them into any important mechanisms etc. Also if they are not welded, I think I might reverse the bolts and glue the bolt heads to the underside of the flap and exposing the nuts. This should make it easier in the future.

John, I hope you resolve your heater problems. Eventually I have to free up my heater valve (including a new "O" ring) and replace the red lever. At this point I don't have a replacement lever. My car is an early 250sl and has the hard plastic transparent coloured levers.

Bernt again: the airflap tilts all the way if you lift up the spring ot top of its middle to free the cable mechanism. The bolts have no loose nuts underneath.

The nuts on the main flap are welded to the underside of the flap. Unless the welds have broken (very unlikely) you should be able to remove the bolts and nothing will drop into the cavity. Take note, that each of the bolts has a washer under it which may stick to the flap. Don't let the washers drop into the cavity. The cable that moves the flap can be adjusted, but a 45-degree opening is about right.

Bob - don't worry about removing the bolts. I did this twice a few months ago (removing this flap) and there's no danger. Actually the space ("box") below the flap I recall is pretty easy to retrieve things from, even if you would drop a bolt, so long as it is not in one of the two small drain pipes (but again the risk of something like that is remote).

I am not sure now but I believe the nuts are actually welded in the car body, so you can't (but also don't need to) change the set-up. The 45-degree angle is ok. While you have the thing open, check whether the rubber gasket is around the flap, and is in good, flexible and fresh shape. Mine had become hard and brittle, so I replaced it. Better seal when you don't want outside air (or water!) in. The rubber seal is a bit odd-shaped, and you need to make sure you have it in right side up (I didn't at first, which is why I had to do the remove-the-flap procedure twice!)

Hi Bernt, John, Cees, that is exactly what I wanted to see. Knowing what to expect,I can confidently do the job. I intend to sleeve the drain tubes with plastic tubing and seal them with silicone around the top. This should eliminate any future rust problems. I also intend to replace the filter if it is still there. At this point I have not enquired about local availability of the original filter. Have any of you made your own filter? Are these filters standard mesh? There must be standard mesh material that can be cut to shape.

Cees: the filter is a mesh type that I just rinsed out, it looked good enough not to have to replace. If it is not there you should be able to make one quite easily from e.g. kitchen hood filter material or something like that, it is a sort of standard and not too fine mesh. You should be able to get one there though, I would think, Ohterwise buy one abroad and have mailed by regular mail, it is very light and should not trigger import duties, VAT or other complications like that. If you can avoid sleeving the drain tubes I would. It limits capacity and also moisture could settle between the metal tubes and the new plastic sleeves? I replaced the rubber hoses underneath the dash and checked that the metal tubes are still ok. If your metal tubes are not ok, then you're probably better off sleeving them.

Bob, I got a quote several years ago of $80.00 US for the filter. Mine was a fiberglass mesh with a metal spring to hold it in place. I simply bought a fiberglass air conditioner filter at a harware store and cut it to shape.

Rodd (on removing and refitting the rubber seal around the fresh air flap): been there, done that, got mad, then got it right. 3M Rubber Adhesive and 3M Rubber Adhesive Remover are critical. (On the filter): Bob, These filters are VERY expensive, probably $80 here in the USA. I made my own out of a cheap ($4) furnace filter. I think it's only purpose it to keep bugs and large debris (leaves) out.

John Hassle: over the past few days, I've been working on my heater core and control cables. During my last road trip, I noticed some water leaking into the car and dripping on my feet. It only happened during heay rain with the air scoop open. I checked the drain tubes and made sure that they were clear and that the rubber hoses were good, but the leaks continued. Today, I found the cause. Three of the heater control cables go through the air scoop compartment and each has a rubber grommet in the firewall. In my case, all three of the grommets were broken and allowed water into the car. I changed the grommets and voila, no more leaks. Whenever you're working on the heater controls or looking for leaks, check the grommets.

Bob: hey group, I did the air vent clean out today. Under my dash I can see rust marks on the firewall paint so I used clear plastic tubing to sleeve the drain pipes and rubber tubing. I used silicone to seal around the top of the tubing. The air filter was in place but it was lying in the bottom of the air well. It was in reasonable condition so I cleaned it and let it dry in the sun then I clipped the spring on the back of the filter into the retaining clips on the body. Funnily, the filter does not extend the full width of the air well.

The vent seal was in good condition and I could not see any rust in the air well itself. I also took the opportunity to replace the plastic tubing to the windscreen washer pump and reservoir tank. On Sunday I did a short trip around town including a stop at the hardware store for 10 minutes. QUESTION - do the black plastic inserts of the chrome pieces that are on the bottom of the door and the front fenders fall out when they become hard? OR: Does it take a screw driver in the hand of some mean spirited sod to prise them out even if they are old and hard?

Look for a little trickle in the lower inside corners of the rubbers, next to the glass, front and rear on the hard top or sedans. This can soak your backing mats and not get the actual carpet wet enough to show it.
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