I'm trying to diagnose a coolant leak on a 1995 Chevy Corsica V6. Just below where the two heater hoses enter the firewall, there is a rubber spigot coming out of the firewall. It sticks out maybe a couple of inches, then bends 90 degrees to point at the ground. It's open, i.e. no valve, no cap, no hose attached. The car recently started leaking a significant amount of coolant out of this spigot (for lack of a more descriptive word). It's a steady trickle when the engine is warm.
What is this thing?? I can't find the answer online anywhere. I've never heard of a heater core having an overflow drain.
Thanks, ~kevin