So its time of the year when we get rain 6 days a week here in WA, and so my 85 gsl se starts leaking somewhere. There is a big wet spot on the passenger floor. I checked to see if it was sticky and smelled like coolant, which it did not. Its water. This happens when car is left parked outside during rainy days. I checked to see if its coming from the windshield: checked/felt underneath the dash, and its all dry. Seat is dry. Pulled the carpet off and its only wet on the bottom, sides are all dry. Also after I first noticed this, I dried everything and laid a plastic bag on passenger floor. After several rainy days the bag was dry, but carpet was wet underneath. Is there a way water can get under carpet or sheet metal? Is the floor hollow inside? Any ideas?

 

I've caused a few people to wet the passenger side as well. Do you have the sunroof and is it draining properly? Leaking through the cowl or firewall may still be an issue. Try using a powder to dust the surfaces. That should allow you to track down the water flow.

 

LOL, that was great. Im going to try powder.

 

Get a smoke machine and place it inside the car with windows and doors closed. When you see smoke coming out, you have found your leak. A flashlight helps.

 

Seriously? I doubt that will work for interior

 

It's probably the sunroof drain which has either come loose from the sunroof gutter on the inside, or from the vent right behind the B-pillar. If the drain comes loose or the hose cracks, it will leak any water that gets into the sunroof gutter to run down behind the passenger seat in front of the bin. That water would be felt under the passenger footwell area in that case.

Try removing the vent/drain at the B-pillar and hope it's there, otherwise, you'll be pulling down the headliner to get to the sunroof drain. Good luck,

 

Another possible source for the leak is from the heater core/AC box. There's a drain at the bottom of this box to get rid of condensation that builds up while the AC is running or if rain water gets in. If the tube for the drain is disconnected or cracked, it would soak the passenger floor when it rains.
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This

 

Heater core and sunroof drain are all good, I checked those first thing. I think I found my leak thanks to Richard I used powder milk and just got it all over the floor with carpet off, then simulated a rain with my garden hose. My exterior A-pillar had a hole under the metal trim. Removed it and sealed with automotive silicone. Now waiting for a-pillar clips to arrive so I can snap the trim back on.