[911monty]

Ahh Good. Yes the purge and bleeder valve are the same thing, it has the wire bail on it. It's purpose is to purge or bleed the air from the top of the radiators and oil cooler so the system is completely fluid packed.
Now the two sources for coolant draining out the drain/overflow hose are the coolant cap and the purge valve. The drain hose attaches to a nipple on the tank which drains this area. The hole is just forward of the purge valve, hard to see but it's there. If the fluid is coming out of the drain hose then one of those two points must be leaking. Do not install the plastic cover over the purge valve. This way next time you hear the hissing open the trunk and see if you can tell which one is leaking. Again if the cap is leaking do not attempt to tighten until the car cools off. Better?

If the cap or purge valve are not leaking then perhaps the hose from the oil cooler you replaced the fitting on is leaking???