Fog on the inside windows....

[Fast Eddie B]

...60’ Plymouth, if it has sat for a while and I drive it with the defrost on (or heat in the cold), the windshield steams up after about 5 minutes, in the next 10-12 minutes, it is all dry. If I drive it every day or so after that, with the heat on, or off, doesn’t happen. Had a 78 NYB did that too.

I know it usually means heater core, but I had the heater core pressure tested before reinstalling. No water leaking in the cab and no loss of water in the rad.

Is it possible that condensation is building up in there and that is the moisture that is getting driven off? Or, am I delusional and it is the heater core...

 

[Pete Kaczmarski]

Touch the condensation on the inside of your windows and smell your fingers and feel if slippery like oil feel. If so it's anti-freeze. Also, the inside of your car would smell like warm anti-freeze if the heater ran awhile.

 

[CBODY67]

In some situations, not unusual for residual moisture to accumulate in the heater box. When the car is started and the fan starts, the moisture will end up on the glass until it cooks off, or you use a clean towel to wipe it off. Just the nature of some of the beasts in certain weather conditions, it seems.

If the water is "on" in the heater core all of the time, then a cable-operated water valve might be an option to keep the heater core cooler before the engine stops?

CBODY67

 

[Fast Eddie B]

Sounds like my suspicion is likely correct - residual condensation in the heater box. Not going to worry about it.