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So you are saying this is not an external leak, ie coolant under the vehicle?

 

Have you identified exactly where the coolant is coming from? A failed water pump will weep from the small hole below the shaft.....if its leaking elsewhere then let us know. If you have not checked for the source, then check all the frost plugs, hoses and thermostat housing.

 

I get that it can be hard to see in there. Perhaps you can remove a few things to get more light inside the engine compartment. Engine cover, coolant storage tank, air cleaner, etc. Until you can see where it is coming from you are just throwing darts at the problem.

 

Check your heater control valve & the hoses for the heater core.
Radiator tanks?
Hoses?

 

Check for the easy spots first... like in this video

 

I wish there was a definite answer for you as I am in the same boat. I have a 2001 Express with a 350 in it, 190,000 miles and I can't get the water pump to seal at all. I bought a good replacement from NAPA and have changed the gaskets 2 times now. When it gets cold out it leaks like crazy between the block and the water pump, I have put a pressure tester on it an confirm the leaks is there.

 

Does it blow white smoke when you drive it?
Does the windsheild for up easily?
is the floor wet in front of the passenger seat?
Does it have rear heat?
Is the floor wet back there?
What size motor?

 

This thread should be locked since the original poster has left it for 2 months. As for Indy Pace Car's comment, he should start his own thread. But, in both cases I would ask if the block mating surface that the pump connects too is damaged or contaminated with old gasket material?