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Pontiac Bonneville Water Leaks



  • I believe that the water leaks came from the sun roof. I replaced the front two with clear tubing that fit inside the existing corrugated tube very well. The two rear tubes were solid but clogged. The flexible plastic grass cutting line worked well until there was a clog that was stuck. Some compressed air in a can did the trick there. All seems well now.
  • You've got to find where the water is getting into the car's cabin. I had it coming in at two places -- just behind the parking brake pedal on the firewall and through the driver's door. Put a water hose on the roof of the car and the driver side door and sit inside. I took out the carpet and the driver's seat so I could find the leak. It's not hard to take out the seat but the center console is a bit difficult. Be patient and take your time. Don't force things or you'll break them.

    If you've got the firewall problem, that's easy. I put some silicone sealant in the hole and it stopped.

    If there is a leak coming into the cabin through the door (you'll usually see it coming in between the door panel and door frame, you've got to pop off the door panel. Use some plastic tools from Harbor Freight (cheap) and pop off the door panel - take it slow and easy and don't break the clips that hold it in place.

    Inside the door is a plastic shield that is supposed to keep the rain water from leaking into the car and directs it down to the drain holes at the bottom of the door frame. What happened to me is the SEAL that keeps the plastic shield tight agains the door frame fails. The plastic shield needs to be removed and resealed. The sealant is the stuff you put on your replacement windshield. You can get it at the auto parts store. It comes in a box and is a long string/bead of sealant. Remove the old sealant on the plastic shield and put the new stuff on. It's real sticky and adheres beautifully to the metal door frame.

    Reinstall the shield, put the door panel back on and let it cure for a day. Try the water on the door again and see if it leaks before you put the carpet back in.

    You might try your other doors for leaks too. Three of mine leaked.

    Good luck.

  • i pretty much have all the problems people have been having on this forum. i need that email with help...any help will do, i have water everywhere. All drain tubes are clogged and wont blow out. Im thinking about putting new tubes in. is my email
  • kts0347kts0347 Posts: 44
    edited February 2012
    I had an 02 Bonneville that had almost all the leaks. Here is the most likely culprits:

    1) Sunroof Drain Tubes: There are four drain tubes running down the four corners of the cabin. They block up and then water overflows the drip pan under the sunroof and flows down the pillars to the floor. DON'T Attempt to blow them out with an air hose. They consist of several sections friction fitted together and the air pressure will just cause the sections to separate and then it's a big problem, requiring a whole lot of trim to be removed to join them back together again. The source of the blockage appears to be small molded nipples at the very ends of the tubes. These nipples are like lips that are designed to be normally shut to prevent insects from creeping up the tubes. They are supposed to open with water pressure buildup. But like all things rubber, after several years, they become either brittle or sticky and then they don't open anymore. The solution I applied was to simply trim them with a scissors. Sounds easy right? Not so, they are in very awkward positions. To access the two front lips, remove the plastic inner fender by pulling out three plastic pins. Remove the inner fender briefly and you will see a black rubber fitting on the rear side of the fender, exiting out of the firewall/cockpit sheet metal. You can trim the lips from under the fender. Water might even rush out as you are trimming. The rear drains are accessed from the trunk, by removing the side inner trunk liners. You will see a tube coming down over the rear fender wells, and terminating in a large black plug right behind and at the bottom of the fender wells. Pull the plug towards you into the trunk, and on the exterior side you will find the offending lips. Trim them off, replace the plug and you are in business. The sun roof leak should be fixed, unless you have disconnected the tubes somehow during your tweeking. If you still have problems, you will have to drop the headliner and pillar trims to inspect for separation problems.

    2) Door Trim Leaks: Water flowing down the window channel will actually flow into the passenger compartment instead of through openings at the bottom of the door, due to the slope of the door. To prevent this, Pontiac sticks a plastic sheet over the door inner to trap the water inside the door and force it to exit out the openings. Over years, the mastic sticking the plastic sheet to the door inner metal releases, and water flows freely into the cabin. Remove the door trim panel, and apply fresh sealant to the plastic sheet to cause it to adhere to the metal. Don't use epoxy, the sheet may have to be removed in future. Use mastic, and perhaps some gasket sealant.

    3) Backed up condensate tube from the AC: Just like the sunroof drains, the air conditioner has a tube that vents condensate water just in front of the firewall. It also has lips that seal and they can get blocked, which causes the condensate to back up and flow into the passenger compartment. This can usually be cleared from the underside when the car is on a hoist.

    Be sure to clear up your leaks. Beyond being annoying, there is a lot of electrical stuff under the floor mats, and when it gets wet and rusts, you start to experience a host of electrical problems like windows not working, seats not adjusting, etc.

    Hope this helps. There are great tutorial videos on this site and on a related site that can help you with details and photos of the process for removing door trim, etc.

    Updated to correct the URL for Pontiac Bonneville Club.
  • bentstorkbentstork Posts: 1
    I have a 2002 Bonneville SLE, I have owned the car since 2009 and started developing water leaks summer of 2012. The right side of the interior would get wet, both front and rear carpeted areas. The rear especially as that is the lowerst point. I vacummed most of a gallon of water out of the carpet twice that summer. As others have done on this forum I took the time and removed the seats and console and stripped the the soaked carpetting out and let them air dry. I did the wet tests, running a hose on the outside. I discovered 3 leak sources and fixed two of them. The plastic shield on the front right door was the main culprit. Everything seemed fine and good over winter and even in this spring until recently. But again wet floors. So again I stripped everything out and started over. The leak now is coming from under the firewall in the extreme right corner. I have no idea where from and really don't wish to strip the dash down. Does anyone have any idea where it is probably running in and if there is a easy fix? Thanks
  • kts0347kts0347 Posts: 44

    I had a 2003 Bonneville and had ALL the classic water leaks. Glad that you have conquered the leaking door seals. They will all become loose in time and a good sealant is needed to cause them to retain a relatively permanent bond. I initially tried household sealants and they survived only a matter of months before re-releasing. Save your energy on a repeat repair and get a good automotive bonding product such as I describe below, from an auto supply store.

    You didn't mention whether you have a sunroof, but the source of the current leak points to sunroof. There are four vent tubes that drain water that enters the roof around the perimeter of the sunroof. It's not designed to keep water out. Rather its designed to drain the water off. There is a drain pan surrounding the sunroof, and there are four drain tubes. When the tubes block, the pan overflows onto the headliner, and flows down inside the trim pieces until reaching the floor. The front of the roof is the lowest point hence the water drains off the headliner into the windshield A pillar trim, then down the side kick panel trim eventually finding the carpet.

    Two tubes route down the front windshield pillar, out through the sheet metal on the side kick panel under the IP, and ultimately dump to the open air behind the plastic inner fender panel.

    The other two route down the rear window pillar, into the trunk and then dump to the open air behind the wheel well.

    I initially thought that the tubes were plugging with debris and mud, and I tried dropping the head liner and blowing them with compressed air to clear them. Bad idea. They aren't a single run of tubing, instead they consist of a series of tubes that are interconnected one inside the other (pressure fit). Blowing with compressed air simply causes these connections to separate, and then you have a real problem getting them reassembled and have to remove a lot of trim to access them.

    However after much work, I finally found that the real blockage wasn't inside the tubes, it was at the very end, exiting out of the car. The engineers designed the tubes to pinch shut to prevent small insects from entering the vehicle. The weight of the water accumulating in the tubes is supposed to provide sufficient pressure to open the pinched ends and it works - when the hoses are new. After several years these pinched ends become a bit sticky, and simply don't open and thus the water overflows. I solved my sunroof leak problem permanently by simply clipping off the pinches with a wire cutter. The rear ones are relatively easy to locate. Just pull off the trunk side trim and you will observe the hoses snaking down and over the wheel well and finally making a tight turn to exit the sheet metal. There is a grommet on the end of the tube where it exits through the sheet metal that you can pull out to reveal the pinch point that you want to snip. Just push the grommet back in the hole and the job is done. In order to remove the side trim, no tools are needed. The hard plastic piece crossing the back of the trunk has to be removed by hand unscrewing some black plastic knobs. There are some similar black plastic knobs securing the side trim.

    The front tubes are a little harder to access. The plastic inner fender has to be removed. This can be done with the wheel in place with a little practice. Pull out the plastic push clips around the fender opening perimeter and the inner fender will be loose. Then just try to get the rear part of it free so you can access the hose exit point. You can snip the pinch point off with the hose in place in the sheet metal.

    Then test the whole system with a hose and ensure that you get water flow on all four corners. Just look for puddles on the ground since you won't be able to see the actual hose ends.

    PS: There is the same pinch system on the end of the hose that drains condensation out of the air conditioner. This can also stick and cause condensation water to overflow the HVAC and leak into the passenger compartment.

    Another source of water leaks that I encountered was in my trunk. My spare tire well would fill with water. I discovered that water would leak at the rubber weatherstrip. Not over the top - instead under it, where it was stuck on a sheet metal lip. The solution was to pull it off, and reseal the weatherstrip to the lip with a good dollop of glue all the way around. I used Pro Seal brand black RTV silicone Instant Gasket, that I purchased at the auto supply store.

    I also had two other sources of trunk leaks. The tail light attaching studs that pass through the sheet metal are secured with nuts backed with a mastic. Eventually they started to leak. The Instant Gasket worked here too. The final source of trunk leaks was the rear window itself. The mastic used to secure the window eventually developed leaks on the lower edge due to the design that accumulates water. A coating of sealer from the inside of the trunk provided a clean finish outside and solved the leaking problem.

    Best of luck. I operated my car in the heat and rain of Florida, it was black color and I kept it outside 24/7 for its entire life so it endured the ultimate of endurance tests. Ultimately all the factory seals failed but fortunately they were detectable and easily repaired - - if I only knew where to look and what to do. The discovery part was the big time consumer. Hope this write up helps you to shortcut the repair time.
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