I bought a clear set of mats to keep my carpet clean in my 70 442. I notice after cruising around the passenger side front and back mats both steam up underneath. I never realized how much heat came up from the floor. I guess there is moisture in the carpet. I would hate to see the floors rot out from this moisture. I now remove the mats to air it out when I am not driving. I have original manifolds and 2 1/2 exhaust. I don't see it on the driver side. Is this common? Anyone else notice this?

 

Sounds to me there is some moiter getting into your car either by a hole in the floor, or window and/or door seals.

 

moiter?

Pull the carpet away from the heater box on the passenger side to check for signs that the heater core is leaking.
Has the car been recently washed or has sat in the rain?

 

Car has never been washed. Just waxed. Garaged and has never seen rain or snow. Floors were redone and painted and new carpet. I checked under the carpet by the heater and it looks ok. I'm not saying there was alot of moisture. Just steam on the underside of the matts. Carpet feels dry. Could be humidity in the carpet.

 

Any coolant smell? Heater core sure seems like it would be the only moisture that could find it's way into/under carpet if car never gets wet.

 

You must be in a hi humidity area for the mats to fog then. I don't think it's a heater core as the coolant should not make to the backseat area.

 

If it's not coolant, then it's just condensation. There's a lot of moisture in the air. When there are temperature differentials, you get condensation. You probably have some moister air trapped under the mats, and now that it's getting colder the moisture is coming out. A can of Damp Rid should help.

 

Depends how fast he accellerates!

 

Check the heater core good! Look for a drip or any moisture at the bottom of the heater box. The core can seep and drip a little before it is noticed--ask how I know--