I'm having trouble locating this leak. When the engine is on, there are drips of coolant leaking from in between the firewall and the bottemside of the car (green arrows on pic). There is a tiny little gab there. There is no leak in the hoses to the heater core. The firewall itself stays dry. The connection of the hoses to the heater core are dry. There is no leak in the interior, the heater core box is dry and the heater core itself is ok (so i did all this work pulling it or nothing )
I hope i explained this properly (English is not my natural language).
I'm all out of anwers, so i'm counting on your expertises. Thanks.

 

Have it pressure tested, maybe its a fine steam (possible to hear it) that you can't see when its running.
To open the hood alot more, so you can get a better look, unhook the hood struts, the hood will go up nearly vertical.

 

Re-installed the heater core and hoses and ran the engine long time. No more leaks.
So maybe there was a leak just where the hoses mate the pipes of the core but I still can't understand that so much coolant could run not along the firewall in the engine compartiment and not in the heater box but in between. So i fear that the leak eventually will return.

 

It might be leaking where the hard line meets the short hose that goes to heater core. It's a return that comes from the Hester core and then runs back up to the radiator for return. I would check to make sure the hose is tight on the hard line where the hose connects to it you should what I'm trying to explain.

 

Dude thats crazy I have the same leak! I think it may be the heater control valve on mine, although the valve is a little further forward but still it could run down the body. Passenger side, right? My intake has a small coolant leak too, which could also run down the body if it gets behind the engine.

 

Check the back of the intake manifold. I had a similar leak. Took me forever to figure out where it was coming from. You can't see exactly where it's coming from unless you remove the plenum, runners, etc. Of course, you'll have to remove the intake manifold to fix it. Doing this project right now.

Steve