Okay, I changed out the heater core on Saturday. All seemed well. Pipes lined up, O-rings looked good, don't remember seeing a leak at the firewall...all back together now.

Drove it briefly Saturday, cranked the heat (all was well). Topped off the coolant to the Max line. Saturday evening I ran an errand and the coolant light came on for a brief second when I started the car (didn't think anything of it because it went off).

Drove it for 20 minutes on Sunday morning and hadn't drove it again until I went to work today. Weather was about 20 degrees this morning, had the heat on all the way to work. Just left to grab some food at lunch, coolant light came on and stayed on for a few. Pulled over, popped the hood...coolant is below the Min line. Felt the floor board on the driver side, feels dry. Felt the floor board on the pass side, still feels a little damp. Not sure because it hasn't dried or if it's still leaking over there.

If it's leaking on the pass side still, where could it be coming from?

I am going to check the ground after while to see if there is a leak under the car too.
Thanks!
Heather

 

If it was leaking from the heater core both sides could get wet.
I would have the system pressure tested.

 

Well, I got home and pulled the carpet back and all before I lost daylight. I did use the flashlight to look against the firewall under the hood and the heater core "pipes". I see no wet leakage. I didn't see a puddle under the car either.

Where is my stupid coolant going?!?!?

 

You might have lost enough when you removed the heater core to create an air bubble and now the bubble is gone.
Top off and see if you lose anymore.