88 z24 stall problem HELP PLEASE

I have an 88 z24 with a problem that is baffling me. The car starts fine but once it gets up to about 45degrees it shuts down. Sometimes if i have it revving at a high enough rpm i can build up the temperature to 90 degrees. I have replaced the different inline filters on the systems already. But once the vehicle stalls out it will not restart until it has been sitting at a bare minimum of 5 minutes. also i have noticed recently a large amount of water at the tailpipe, but i have put in a couple bottles of methyl to help eliminate the water problem but it doesn't seem to be working as well as i had hoped. I have checked the head and it doesnt appear to be a blown gasket, the vehicle sounds actually very good until it quits. the longer i leave the vehicle to sit without putting power to the engine, the longer it seems to run. if someone could shed some light into this i would be extremely grateful