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Leaky Mustang is making me weepy

I’ve got a 2005 Ford Mustang Roush that has developed a mystery water leak. At first we thought it was a problem with the cabin filter when for no apparent reason, under clear sunny skies, a waterfall emptied on my husbands feet when he drove up an incline. When checked the suspect filter was cleaned and for a time things were fine then we kept finding the floor mats and rug in both the driver and front passenger side soaking wet with up to 1-2 inches of water! Since it was now the rainy season here we suspected the cause to be possible clogs in the small drain opennings by the wipers. These were cleaned out and again within weeks there was water in the car again. We then tried checking the windshield thinking perhaps there was a bad seal. We spent almost an hour running a hose over the car while one of use crawled around inside with the carpet pulled up and a flashlight looking for water coming in – nothing!
We and our mechanic at a complete loss for why and how the car keeps leaking.

Start with the area under the grill right in front of the windscreen. There is a drain there and if the drain is blocked, you end up with water in the car. You have a classic case.

Af course there is more than one possibility. Do you have a sun roof? If so I would rate that just as likely.

I’m betting the drain tube for your a/c is plugged. A glass of ice water will sweat and drip just sitting on the table. Your a/c evaporator does the same thing. This part is inside the car under the dash, and there is a drain designed to let the water drain to the outside. If that drain gets plugged–wet carpet. It may even seem worse in rainy weather because the a/c is running anytime the defroster is on and it’s already humid.

Have your mechanic check the drain.

I believe that asemaster is correct.
Have your mechanic check the condensate drain for the A/C system, and–if necessary–blow it out with compressed air. More than likely, this will resolve your problem.

Thanks for the suggestions - keep them coming !

If you think the leak is rainwater and not a/c drain water, try this. Start the car, turn the fan on high vent, fresh not recirc, shut all the doors and windows. Take a spray bottle with a mixture of dish soap and water, and spray all around the window seals, door seals, windshield, sunroof, etc, anywhere you think water could leak in. If there’s a leak, the escaping pressure from in the car should make bubbles.

I’ve seen quick oil change places place a bolt in the drain tube to keep it from dripping on them while they change the oil. This causes the back-up that asemaster talks about also but could be the cause.