1989 Chevrolet Corsica 2.8. Draining and especially bleeding the cooling system
 

Hello.
I have a Modelyear 1989 Chevrolet Corsica with the 2.8L V6. I had to replace the thermostat and the waterpump. At the same time i wanted to replace the coolant.
In my case i was unlucky and my radiator had no petcock, so i had to pull the lower radiator hose. I drained around 5 Liters from the radiator and what came out of the engine (Not counting in from the reservoir), but in the manual it says, the whole cooling system holds almost 16 liters?
Is it possible to drain the engine block? And if so, where are the bolts?

The next thing i am concerned about is bleeding the air from the cooling system. In all the manuals it says, loosen the bolt on the thermostat housing. But there is no bolt? On top is something round, but the whole thing is one piece. Nothing to bleed there?!
Can someone help me with my odd questions? :D

Greetings Alex