Coolant leak under car from heater system

[Sept]

I discovered today a significant drip/flow under the car on the driver's side after I had used the heater.  I'm wondering if anyone else has seen this. It is engine coolant as best as I can determine, it has no odor I can detect.  A previous owner installed a cut off valve on the hose that flows from the engine block into the cabin interior that carries engine coolant into the interior of the car for the heating system.  Until recently this valve was closed and the heater levers in the car set cool.  The flow was coming from about 12" from the edge of the car so it pooled there and was leaking/running out.

Now I know why the previous owner had this cut off valve installed...  Is this coming from the heater core?

[Jonny B]

The first thing to check would be the heater control valve that is accessible from the large circular grommet on the top of the firewall. You should be able to gently pry it off to take a look at the valve. If it is leaking from the valve itself/o-rings, you should see a tell tale.

If that shows no signs of leakage, then it could be the connections to the heater core (or the hose ends), or the heater core itself. But I would think the heater core leakage would be inside the cabin.

I just tried the search function (it is your friend) - use the main search page, the fourth item, to the right of the "Home" link. I used "heater core leak" - no quotes though, and it was less than a page of items, but the first several might help.

[Sept]

Thanks

[Sept]

I’ve read through several threads on the heater core and looked at the images from the old Yahoo content. In looking at the heater core no one has talked about what seems to be a fluid return line on “left” passenger side of the heater core.  Where does this line flow once it leaves the heater core? In trying to trouble shoot the leak I found yesterday I heard what sounded like fluid coming from the heater core on the passenger side (with the hood raised).  This could be the source of the fluid that was running from underneath the car on the drivers side although there was a smaller drip toward the center of the car underneath.

[Jonny B]

Not exactly sure what you are writing about. There are two lines at the core, one on the left (by the brake booster on LHD car) that has the heater control valve. This line leads to the head.
The line on the right (on the passenger side) flows under the intake header, to the water pump, near the alternator. One or the other, or both could be weeping/leaking at the hose connection point at the firewall.

[Sept]

Thanks.  I see the line coming from the passenger side from the heater core back to the radiator and no sign of a leak there.  The previous owner installed a manual valve on the inflow line which I’ve closed but I still get wet spots under the car from the same location after I drive it although not as bad as prior to closing the manual valve.  I’ve also adjusted the heater levers such that the heater core valve should be closed if it’s working properly.  My conclusion at this point is i’m getting some flow past the manual valve into the heater core still.

[Sept]

For anyone interested in this that has a heater core leak issue. 

The baffling part of this issue was the continued coolant leaks under the car after I closed the input valve several days ago. This area of the car must have a water drain that allowed the coolant to flow to the underside of the car.

After gathering suggestions on what might be the continued source from two reliable maintenance shops they suggested the outflow line to the water pump was sending coolant back to the heater core.  I installed a shut off valve in the short line coming from the outflow side of the heater core to isolate the core and finally the leaks under the car have stopped.

The core will be replaced when interior restoration work is done.

[Jonny B]

Thanks for the update. Probably a wise move to push the core repair to the same time as the rest of the interior work. Removal of the core is a real pain in the back kind of job.