We had a bad rainstorm and my drivers side floorboard is completely soaked. My window was up and my door seal is okay. Where would the rain water come in at? Is this a common problem?

Windshield Seal, maybe enve HVAC inlet, who knows.

Maybe your heater core is leaking?

its water right if it was a heater core wouldn't it be green coolant on the floor

Yes, water from a massive storm. It's not the windshield seal, is there any place to leak under the dash through the inlet vents? If so, what seal is bad and where is it?

sun roof??

Yes the sun roof has drains that can get clogged. Check those out.

I found the same thing with my mark which had been sitting outside. The passenger side floor was soaked and a little moldy. I dried it and then pulled up the carpet and dried and cleaned it underneath.

happens to me too.

got the same problem... hate it very much. mine is passenger side also, but i notice one of the plastic cowl screws is missing on mine...

I am told that the rubber seal around your fan get's brittle ,cracks and leaks. If you open the hood look through the vent by your windshield you will see the motor and the seal. they told me to put some plumbers glue around it but I haven't figured out how to get in there yet.....

Check the rear floor pan-look under your car and you will see on each side a black alongated rubber grommet-pop it out and make sure it is seated all the way around-sometimes they curl on one side and let the water in :mad:

Your cowl is leaking. Same thing happened on my Charger before I got her restored. It's not like Mark VIII's aren't known for rusting.

The rain gutters from the sunroof often recede into the body and the water is channeled into car instead of outside. A real annoyance. You should check the regularly.

I agree with above. Those moon-roof hoses can actually come off, but for whatever reason it happens a lot on the passenger side from what I have read. Then the rain water will run down the pillar and into the floor.

Not easy to get at, you have to remove the pillar cover and trim above the door as well as the strip around the moon-roof opening. and carefully peel the headliner back enough to see. Flash light will help a lot.

The window seal can go, but you usually need water pressure to get through, like a car wash.

Other item would be the air-intake for HVAC. Located on the passenger side it looks like a bowl or tube upright. Remove the wiper blades by pulling th tab outwards - not off - and pulling up on the arms with a rocking motion. Should only have to do the passenger side. Then removes the three or four black head screws holding the plastic cowl cover down. Open the hood and just pull on the weather-seal that runs along the back forwards. It will pull off and that s about it. The cover will come off and you will have some access to it. Pour something around the base of it.

I had the same exact problem after a week of nonstop rain.. I soaked the carpet with Lysol to prevent mold. It worked, but for the next few days I was afraid of getting pulled over because it made the interior reek of alcohol. :p

The moonroof drain sounds like a likely culprit. How many drain hoses are there, and where do they run?