1993 100CS. The heater core was replaced a couple weeks ago. Some days I will come out and there will be no antifreeze on the ground and other days there will be a pond of it. I can't figure what where it is coming from. It seems to be from the back of the engine because I can't see any drips on the front or either side of the engine. Any have an idea of what it could be and a possible fix?

will drain off the undertray at the rear so the leak could be anywhere.

You could try removing the undertray for a few days to see exactly where the leak is.

My undertray isn't in place and it is coming down onto on of the back screw holes for the undertray on the driver's side

where is the expansion bottle? I am assuming the core plugs are fine because the heater core ws just replaced. The water pumps shows no signs of leakage

If you had heater core replaced, you may want to remove the cowel cover over the fan box and core and check the hose fittings clamps that they did loosen up on you! If it is leaking from a fitting or bad heater hose the antifrezze will leak down through the drain hole and appear to be coming from back of the engine! Happened to me after core replace!! Look and make sure it is dry around the fan box area!

Smokie

Is it the tank that you fill up with antifreeze?. The kinda of square looking tank?

Ok here is an update. It's leaking back towards the firewall in the enginebay. No sure where it is coming from. Could it be the water pump? Or is it more likely to be something with the heater core. I just had the heater core replaced and the mechanic said it might be the valve on it.