Heater core leaking inside vehicle - 1994 Cadillac DeVille

The heater core is leaking fluid inside the car. The heater core needs to be replaced. Feel the liquid it should feel slightly sticky and have a slight sweet smell to it. Open the hood and look in the antifreeze reservoir. The liquid should match color and consistency.

Sounds like the heater core is leaking. The heater core is located inside the vehicle, usually contained within a plastic box, when the heater core leaks enough, the plastic box will fill up with coolant and eventually leak out, usually onto the passenger side floor. Hope this helps.

Either a hose isn't tight or has a crack in it. You could also have a defective heater core.

It is not smoke though it appears so. It is thick heavy steam from a coolant leak in your heater core in the cabin area. It will smell very sweet if it is a typical glycol based antifreeze, and the windows will fog up as the hot coolant enters the cabin area of the vehicle. Primarily on the inside of the windshield. The cure is that your going to have to replace the heater core as it is leaking. Do this soon because if it ruptures completely you will have a major mess on the floorboard of your vehicle. Coolant is also poisonous to humans and animals if ingested. The heater core will be a little pricey as will the labor to replace it. Good luck. I guarantee you it is the heater core leaking.

Leaking inside sounds like the heater core. If the core is broke right where the heater hoses connect, it might be losing coolant down both sides of firewall, inside and outside. Otherwise, look for a leak at the intake manifold. That might run down back of engine near the transmission, as you indicated.
Good luck.

Water or coolant? inside the driver compartment or under the hood? if it is inside it sounds like a leaking heater core

Dear Foggy Film......
You are correct!!! This foggy film is the result of the antifreeze leaking and then evaporating inside the cab of the vehicle. The heater core on this vehicleis located inside the evaporator case inside the vehicle's cab on the firewall up underneath the dash closer to the passenger's side. It involves about three hours labor to replace the heater core.This is a moderate to mildly intensive repair for the first timer..if you have any more questions then you're more than welcome to get back to me!!!! HOPE I COULD HELP!!!

There is a chance you may have an engine bay coolant leak and the fumes are being drawn in through the heater ductwork so verify that first.
But....
Coolant fumes inside usually come from a leaking heater core. The heater core is like a small radiator inside your vehicle that gives off heat.
Problems like this arise from coolant that has not been flushed and creates an electrolysis that eats away at the material causing a leak.
This is not a job for a do it yourself guy(or girl). A pro could easily spend 5 to 7 hours changing this one.
Make sure whoever does this repair flushes the system.

If it's your heater core, unless you're a mechanic you probably should get professional help. The heater core is located on the firewall and many parts need to be replaced to get to it. Do you see water on the floor inside the vehicle, Many times a heater core will leak inside.

Your coolant level should be going down too, so to confirm leak at core, check that. Just in case it's water leaking in elsewhere. Can you smell the antifreeze inside? Does it do it even on dry days, no rain?
Double check hose connections are good & tight where they connect to heater core at firewall. Have seen a couple of bad connections allow coolant to leak inward to vehicle. System pressure test will confirm also.