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Q: Leak around interior fresh air intake can on cowl? on 2000 Nissan Maxima

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Hi folks, I have a Maxima and there's water running into the floorboard when it rains. I removed the plastic cover off of the cowl, and explored this weekend. I can pour water into the oblong opening in the center top of the cowl and the water runs out behind the wheels. Somehow water is getting in the fresh air duct. There is a metal vertical opening about 3 inches high that takes in the air, so could the seam around that be letting the water in??? How in the heck do you fix that??
No car image 94a1663db56199c5353592009e34aaa51078a2469bed068bb8d6f0ba43accf97
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I admire your persistence to get to the root of the problem with your car. I would have thought from what I initially read that water must be leaking in past the windscreen bonding seal. I don't see rust in any of your pictures (great!). Have you tried pulling back the carpets and looking upward to see exactly where the water is coming in. The heater box/casing has a drain tube (it allows the air conditioning system to expel water vapor created the AC evaporator to drain when the air conditioning is working.) Could this tube be blocked? This tube/drain should allow even rain water that enters the heating ducts to drain out. I have seen these block on many other cars allowing water to puddle at the passenger foot well. I have a factory workshop manual at work I'll look at it in the morning see if any other thought come to mind.
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I looked at a factory Nissan repair manual today, they are really good manuals, very detailed and usually pretty good for illustrations. I looked closely at all the illustrations to see if I could determine the exact location of the evaporator/heater box drain but none of the illustrations were clear. From what you have said I think that drain must be blocked with a leaf or some piece of debris. The drain has to be located at the lowest part of the heater box casing and run forward toward the firewall. I have seen some car manufacturers put it at the bottom of the heater motor. If you've ever noticed a car running at a traffic light on a hot day you see a pool of clean water underneath behind the engine but ahead of the passenger foot well. With the car jacked up look for a tube about 10mm in diameter coming out of the firewall in front of the passenger foot well area just above the steering rack or in that vicinity. Perhaps poke a piece of coat hanger (about 2 inches) up there if water shoots out you have found your problem.
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We were just talking about your car at the office Friday.Please let us know what the problem turns out to be as we are all curious. Good luck!
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Thanks again for the update, sound like you could be nearing a successful end to this problem.
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At this stage you must have considered moving to the Arizona or New Mexico deserts, any where with little rain. Good luck. I look forward to hearing your car no longer leaks water!

I currently have the carpet pulled back so that only the metal floor is exposed. The carpet got wet the last time it rained, so I'm letting it thouroughly dry, but also, if we hit a rainshower, I have a towel as a barrier right now. It is tough to see EXACTLY where the water is coming from because it is so tough to see the source, but it is eventually dripping off of the black plastic box/cover that is up under the glove box. It is definitley the passenger foot well. Maybe it IS the drain tube for the heater box/casing? Can you tell me where that drain is located??

Excellent, I'll try to see if I can locate it Saturday and see if that is the problem then I'll let you know. Thank you!
Well, took it to an oil change place yesterday and they checked the tube, and ran a coat hanger into the tube and said nothing was there. Not really sure where to go from here except to a professional.....AAAAHHHH!!
I guess it depends on what it turns out to be if I tell you our not!! I guess I'm hoping it is not a major problem as far as $$ goes, but it is proving too difficult for me to locate, so I'm gonna feel pretty dumb if it's something extremely simple!!!

I'll definitley post the problem.
Well, update...the car spent the morning at the dealership and came up with the same thing I did. There's a leak that can't be spotted without taking the dash out to see where it is coming from. I'm taking it to a body shop on Friday, so maybe I'll have something then. Argh....
Well, took it to my local trusted bodyshop guy, and he determined the leak was in the same area I said, and after blowing a fan down in the fresh air intake hole on the cowl, he used two tubes of some kind of seam sealer that is like a very thick syrum and flows into areas, and then as it hardens it seals off the areas that have leak possibilites. I have not been able to see if it is leaking because he wants it to "cure" for a while, but in a few days I'll give it a shot and see what happens and let you guys know. He did say that quite a few Grand Prix cars have this problem, but he has never seen a Maxima.

Well, 3 days after my last post it was raining, and the car was still leaking. So I took it back to my guy, and he said that after going over the area more thouroughly, he said that it appears that there is an area right at the bottom of the windshield that is like a "tab" or "footing" that provides a little support. This area is on top of the cowl, but what you can't see is that right under the metal is the fresh air duct that goes directly into the cabin. I think this area has the potential to be a widespread problem in the coming years for this style of Maxima. I haven't verified that the leak is fixed, but he said they tested it multiple times and never got a drip on the inside, so keeping my fingers crossed!!!
Are you sure the windshield is not leaking where the lower part of the windshield meets the fresh air intake?
Does your Maxima have a sunroof? Because a clogged sunroof drain will backup and flow down behind the interior trim and end up on the floor. You can mix a little comet cleanser with water until the water turns blue then pour it around slowly in different areas until you see blue water coming in.
Thank you very much for the reply....I'm 100% sure it's not the windshield leaking. I already took it to the windshield shop and they inspected it and said it was fine, and then I checked it out myself also. I tried compressed air from the inside and soap suds on the outside and it didn't blow bubbles.
That was the first question to my wife, but then she reminded me that we DON'T have a sunroof!!

The water is coming in when I pour it in the outside air area on the firewall. I just can't figure out how it is making it through.
That intake air plenum should also have a drain. If there are lots of leaves of plant matter built up at the base of the windshield, this can clog the drains for the plenum tray. This is common for most makes and models. The hvac housing (heater box) also has a drain that may be plugged but that may be less accessible to check. Look in the air intake with a flashlight to look for a drain.

If there is access, direct the garden hose (no pressure tip) at the seams to check for seam integrity. I think it is more likely clogged drains for the plenum
You should not have to cut any body metal to inspect the seam though it might mean you need to remove a lot of parts to get to that seam. Is there a plastic plenum piece at the base of the windshield that can be removed? I can't find any repair guides online but you might consider finding a repair manual to help. If you are certain the seal between the firewall and the heater intake is leaking, I bet you will be able to find the seal from your local Nissan parts department.
Cutting body metal will only open the door to more leaks, and possibly rust. I would definitely avoid doing that
this looks like a decent exploded view of your cowl tray
He could probably move out to California too the way they've been talking drought lately. good luck!
I'm convinced it is the seam integrity around the base of the metal intake "stack". Only problem is that it is enclosed to the extent that I can only see one side of it when I shine a light up in the enclosure. To really check it out I think the metal will have to be cut away on under the base of the windshield!!

There's no plastic under the hood that can be removed after the top cover is taken off. There might be a way to take off the top metal piece that I just haven't found. It might involve some of the heavier duty bolts up under the hood hinges or the tops of the fender. I'll try to get a picture that will show better. The exploded view is decent, but if I only looked at the exploded view, I would have no idea what to expect because it looks alot different once the plastic 4 ft long cover is taken off. (Should I upload a picture to Flickr or is it possible on this site?) THANK YOU
Did you ever solve this problem? I'm going through the exact same experience as you. Was it something around the windshield "tabs"? What did they do to fix it? Thanks in advance.
I, too, have been having the same problem. I thought they fixed the leak this spring when I had repairs done on the AC system (almost $2,000 for new compressor and other repairs) and now, after a dry summer, the leak is back with a vengeance and there is a leak in my trunk and the leak is extending to the rear passenger area. I now hate my Maxima. Will not be buying another one if things don't improve soon.
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