I have a 2005 cobalt ss 5 speed with the 2.0l supercharged engine. I just finished replacing the head gasket and every other seal in the upper engine as well as the water pump timing chains and a few other things.
I bought it off facebook with a blown head gasket. It now runs great with no issues except for a steady drip of coolant off the bottom of the bell housing. It only happens when the engine is under load, not when idling. I got a radiator pressure tester and I
can pressurize the system to about 10psi and it will start to leak. I have taken out the fuse box and felt all around the bell housing, the thermostat housing and everywhere else I can think of, and everywhere is dry. The coolant seems to be
coming out of the bell housing itself. Does anyone know what this could possibly be? I wonder if it is maybe what caused the blown head gasket in the first place if the person let it run dry... Is there anything inside the bell housing which can leak? I am
under the impression that it should just be the sealed block from that point down without even freeze plugs in there.

 

Nothing in the bell housing would be leaking coolant. Something above it is leaking and it's dripping down. My guess is an oil cooler hose.

 

I have looked all around the bell housing and the seem where it mates with the block. I even added UV dye to the coolant and searched with a light and the only place where I can find coolant is the crack between the bell housing and the block on the back of the engine not quite half way up the bell housing. It runs down that seam and drips off the bottom. I don't understand where it could be coming from inside the bell housing, but there is no coolant anywhere else that I can find, and it is pretty obvious with the dye.

 

Unless you have a hole in your block the coolant is most likely originating somewhere else and seeping into the transmission/engine mating seam like ninja said. I suggest taking our your intake, ECU, and fuse box to take a closer look or maybe try a quality borescope. If you did have coolant leaking around the oil cooler is could be very hard to detect that origin because the oil cooler pretty much sits right on top of the transmission without enough space to see in between without a borescope or something.