I put in a heater core in my non ac 88 conv. When I took out the case and old core lets say I was not careful with any fluids spilling. So at that point the black rubber matting backed stuff got pretty wet. After I had it together I had a leak see in the motor dept side of core pipes. Turns out I had one hose pushed all the way up the the fire wall and the clamp in the wrong place allowing rad fluid to shoot back through the firewall hole for the core tubes. I drove that way for a few days before I noticed it pissing fluid back into the heater core box, how much I am not sure. I have since fixed that but still seme to have fluid in the box, I assume from the **** back into it. When this took place prob 8 weeks ago, the exposed rubber/matting backed stuff on the inside of car side of firewal that the box mounts against, when I squish the exposed portions below the box I still get rad fluid on my fingers but at no time do I ever see fluid leaking in the car otherwise. I get NO rad fluid fog in the car or on window via defrost when I drive it which would mean the core itself is not leaking? Does it just take FOREVER for that rubber padding to dry up? Could I have rad fluid STILL sitting inside the box from the **** back issue? When I run the heat it still smells a tiny bit like rad fluid but I think that is just from what is still in the box???
I have been monitoring the over flow tank and the rad, the levels are staying DEAD on, have not lowered at all since the new car was put in.

 

Plan on lifting it and allowing air to get underneath. The rubber not only keeps water out, it will keep it in once it gets in. It is nonporous, and traps the fluid. I had a leak in my 91 wagon, and it took weeks to dry even with lifting the carpet.

 

When you decide to lift the carpet, install a complete newspaper (folded if you need the space) to absorb the excess fluid and change that paper every couple of days until you are satisfied that it is dry.

 

I have lifted the carpet and pulled back on the rubber stuff to allow air to hit it when parked and the heat to hit it when I drive it, which is not a much. Guess it will just take time.