Well, don't know if it is a blown motor per se but you definitely have pressurized air getting back into the coolant system somewhere. That's not good.
Check your oil first. If it looks like chocolate milk, you have big problems.
Best case scenario is you blew a head gasket. They remove the head, put in a new gasket, put everything back together and you're good to go.
If that isn't it, it may be a cracked head. This is common when you severely over heat your engine from lack of coolant. While that sounds really bad, it is a matter of pulling off the head, replacing it and the gasket, and then putting everything back together.
Of these two scenarios, neither one is considered a blown engine.
The third, however, would be. One scenario is your block is cracked somewhere. Worse, if you had bad enough knock (that you could hear it is an indication it was VERY sever) you may have damage to other parts inside the engine. Regardless of HOW bad the damage is, any of these scenarios where the block has received damage and you're best off just getting a whole new engine. Good news is you may be able to sell some of your parts off to other folks wanting to do a turbo kit on their 2.4 Skys to offset the cost of the engine replacement.
