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Pontiac Pond

Hey guys, Marcel here from Mcminnville Oregon. I love your show and try to listen to it every Saturday and Sunday when I can. Here is my question. I have a 1998 Pontiac Grand Prix SE 3800 V6 Automatic and I have a reoccurring water leak problem. It’s been going on for about a year now and it only happens when it rains. On the passenger side there is a leak and water runs from the upper floorboard area where the heat vents are and the heavier the rain the more it leaks. I am wondering if there is a broken valve/tubing somewhere or is something plugged up and overflowing? It has gotten to the point of at least and inch of standing water, but every time I fully dry it out. Also is there an erosion or mold issue I should be looking out for and if so, how can I treat it? Thank you so much for your time.

Do you have a sunroof? If so I would start there. Sunroofs often get their drains clogged (no the sunroof does not seal the water it, it just diverts it to a drain), there is one on each corner. If no sunroof the next most common problem is a clogged drain for that area under the grill right in front of the windscreen. Next is the air conditioner, but it is getting late in the season for them and you indicated a connection with rain.

String trimmer line or a little compressed air are the usual tools to fix a blockage. Don’t overdo it or you can damage the drain system and cause more damage.

Good Luck

The most likely culprit is a clogged AC evaporator drain tube. If the tube is clogged rain, which gets into the ventilation system, or condensed water from the AC, runs into the car instead of out onto the road.

The tube is located on the firewall, low on the passenger side. You may have to get under the vehicle to find it. Use jack stands or ramps if you have to crawl under the car.

If the drain tube isn’t clogged I’d check the sunroof drains, assuming your car has a sunroof.

The padding under the carpet is a sponge-like material, and will absorb and hold an enormous amount of water. You cannot remove this water unless you lift the carpet and remove the padding, which can then be dried outside. If you don’t do that, mold and mildew will grow in the padding. I’m surprised you aren’t smelling it already.

It’s not easy to get under the carpet, but you must if you want to get rid of the water. When you see how much water is in the padding you’ll be amazed. And there isn’t a shop vac on the planet that will remove the water from underneath the carpet. The padding has to come out.

Find and fix the leak first, though.

Some cars also have drain ways in the cowl or gasket/sealant problems that produce the same result.

I do not have a sunroof (unfortunately). I will definitely look into the air conditioning system and maybe using that string trimmer to clear any possible blockage, thank you for your insight and advice.

Thank you for the valuable information. I will locate this problem then go back and dry out those padding’s under my carpet, something tells me there will be a lot of mold buildup though. This was so helpful and being the “do-it-yourself” kind of guy I am, this is really quite more simple than I originally thought.

I will look into that, thank you very much.