FYI FORD MustangSteve's Ford Mustang Forum / Floor pans and condensation

**Posted by Toploader** 6/25/2024 2:59 AM

I'm currently fitting new carpet to my car and noticed what seems to be some condensation on the floor pans in the front, under the dyna matting.
It definitely looks like condensation, or a sweating happening.
Not a big deal, but I am seeing some surface rust, which I will sort out.

Has anyone else experienced this on their cars?

**Posted by RTM** 6/25/2024 3:04 AM

A small leak would be my concern, not sure I’ve ever see condensation build up like you have mentioned.

**Posted by TKOPerformance** 6/25/2024 5:44 AM

I would find condensation to be a curious problem. Typically there has to be some kind of temperature differential to produce condensation. IIRC there's a "dew point" for various combinations of temperature and humidity in the air. If the dew point is exceeded you get dew or condensation. So the question would be how is that happening in only one location on the car?

**Posted by Greg B** 6/25/2024 6:27 AM

Does your car have air conditioning? Not suggesting the drain is leaking but this:

When we drove the family minivan to the bash in GA in 2006, the passenger floorboard was getting wet. I tried to figure out what was going on, I realised the air pressure at interstate hi way speeds was forcing the air conditioning drain water back up and around the foam seal. It drained properly when you would stand there and look at it so I knew the tube was not clogged or kinked. When I got to Carrolton, I got a tube of silicone at the auto parts store and slathered it all around the tube basically making a new seal. It never leaked again.

A Mustang has several openings that aren't particularly sealed well. Heater tubes, condenser drain, come to mind. Just thinking outside the box outloud, that is what I do.

Last edited by Greg B (6/25/2024 6:28 AM)

**Posted by Toploader** 6/25/2024 7:01 AM

Thanks for the replies. 🙂

The car was originally an A/C car, but I removed it 21 years ago and haven't gotten around to putting in a new system.

There could be a leak, but I'd really be surprised. I feel that I've sealed everything up pretty well. Its strange that it's happening only in the front though, but it does look like it's a sweating to me. The water present is a small amount.

The carpet isn't getting wet that I can see. The car is garaged and not driven much in the rain. I don't wash the car all that much either.

This really has me stumped... 🤔

Last edited by Toploader (6/25/2024 7:05 AM)

**Posted by 6sally6** 6/25/2024 8:45 AM

You leave the windows DOWN while in the garage ?
Does your garage floor sweat ?
You have a fan running in the garage?
Do the windows sweat inside the Mustang?/Garage?
6sal6

**Posted by BobE** 6/25/2024 2:39 PM

adding to Sal's post ...
Check the water heater hoses, may have a slight leak?
Check for any water coming from the cowl.
Check all the penetration in the firewall.
Check the seal around the windshield.
Check the floor plugs by the front seats.

This could be left over from a previous leak, drying out under the rugs can take some time unless the car is parked in the hot sun for a long time.

**Posted by Toploader** 6/25/2024 3:36 PM

Thanks guys..
I typically park in the garage with the windows up. I don't see any condensation on the windows. There is no fan in the garage.
The last time I drove in some slight drizzle was maybe a few weeks ago, but the windshield should be well and truly sealed up. The cowl should be sealed too, but who knows.
With the interior out now, I may pour some water around the windshield and cowl to see if I find anything coming in.

Last edited by Toploader (6/25/2024 3:40 PM)

**Posted by Ron68** 6/25/2024 5:00 PM

Do you leave your windows down? Do you have a cat?

**Posted by Toploader** 6/25/2024 8:27 PM

Ron68 wrote:
Do you leave your windows down? Do you have a cat?

I don't leave my windows down or have a cat...

**Posted by Toploader** 6/25/2024 8:35 PM

Earlier today, I poured a large jug of water along the windshield and cowl area. I couldn't find any water coming in down the floors.

With the dynamat material, I never peeled the backing off and stuck it down as I was a bit hesitant to stick it down. I am wondering if this could cause some condensation or moisture to form between the foil and the floor pan?

Currently I am recoating the floors with an oil based black enamel (exterior rust proofing) type paint.

After that, I plan to coat over that with a wax type rust proof coating that dries semi tacky.

After that, I'm reconsidering what insulation to put back down...

**Posted by lowercasesteve** 6/25/2024 10:13 PM

Have you looked for a leak in the heater core?

**Posted by Toploader** 6/25/2024 11:19 PM

lowercasesteve wrote:
Have you looked for a leak in the heater core?

With all the carpet and insulation all out of the car now, I am not finding any leaks running down the floor pans. I still think the metal is sweating somehow, but who knows...

**Posted by Rufus68** 6/26/2024 3:01 AM

In order to have condensation, you need to have warm moist air in contact with a cool surface. You see this on the glass of your chosen favorite iced beverage. When the floor pan is covered, I don't see how these conditions are met. I suspect the water entered the area as a liquid and not as humidity. ...but I can't know this for sure.

**Posted by TKOPerformance** 6/26/2024 5:42 AM

Toploader wrote:
Earlier today, I poured a large jug of water along the windshield and cowl area. I couldn't find any water coming in down the floors.

With the dynamat material, I never peeled the backing off and stuck it down as I was a bit hesitant to stick it down. I am wondering if this could cause some condensation or moisture to form between the foil and the floor pan?

Currently I am recoating the floors with an oil based black enamel (exterior rust proofing) type paint.

After that, I plan to coat over that with a wax type rust proof coating that dries semi tacky.

After that, I'm reconsidering what insulation to put back down...

So the foil of the Dnamat was face down? I'm guessing the black backing was face up? Was the area you saw condensation the only area where this was the case? If so, here's my thought: black absorbs heat. I'm wondering if the Dynamat was getting considerably hotter than the floorpan and leading to the condensation. The air would have to be humid for this, but hey, its summer. There would also have to be a source for the heat (bright non LED light, the sun, etc.).

**Posted by Toploader** 6/26/2024 6:43 AM

TKOPerformance wrote:
Toploader wrote:
Earlier today, I poured a large jug of water along the windshield and cowl area. I couldn't find any water coming in down the floors.

With the dynamat material, I never peeled the backing off and stuck it down as I was a bit hesitant to stick it down. I am wondering if this could cause some condensation or moisture to form between the foil and the floor pan?

Currently I am recoating the floors with an oil based black enamel (exterior rust proofing) type paint.

After that, I plan to coat over that with a wax type rust proof coating that dries semi tacky.

After that, I'm reconsidering what insulation to put back down...
So the foil of the Dnamat was face down? I'm guessing the black backing was face up? Was the area you saw condensation the only area where this was the case? If so, here's my thought: black absorbs heat. I'm wondering if the Dynamat was getting considerably hotter than the floorpan and leading to the condensation. The air would have to be humid for this, but hey, its summer. There would also have to be a source for the heat (bright non LED light, the sun, etc.).

The foil face was facing up. I didn't peel the backing off it, because I wasn't sure about sticking the stuff down.

**Posted by Toploader** 6/26/2024 6:47 AM

If there is water somehow getting in, I wonder what the best thing to do is?

I did try the water around the windshield, cowl and wipers and couldn't see water trails down the floors.

I do drive my car more than most probably do and maybe with wet roads, some water has come in somewhere.

How well sealed are your cars? I'm now wondering if water just gets in and that is how it is with these things?

**Posted by BobE** 6/26/2024 7:26 AM

Remember, these cars are old and never designed to last as long as we have them. So, seal sealer that was used both external and internal could dry up and separate from the surface. So, I would suggest checking the seams in the wheel wells to see if it is still intact, and any other location that could allow water to get into the interior. If you can, take it for a drive in the rain.

**Posted by BobE** 6/26/2024 7:27 AM

Rufus68 wrote:
In order to have condensation, you need to have warm moist air in contact with a cool surface. You see this on the glass of your chosen favorite iced beverage. When the floor pan is covered, I don't see how these conditions are met. I suspect the water entered the area as a liquid and not as humidity. ...but I can't know this for sure.

I agree.

**Posted by 6sally6** 6/26/2024 9:26 AM

To Toploader.......as they say down South..
"Hey brother...where you live at"?! Your info thingy on the side doesn't say....)
6sally6