I took the head off the engine today, thinking that my headgasket was blown and upon further inspection, i noticed that the main coolant passage was completely blocked off with dirt. Now, if that is blocked off, would it explain the fact that the engine would have a crapload of white smoke coming out of it on cold startups? would it also explain the engine wanting to have a TERRIBLE idle quality? Would it also explain the engine wanting to quickly overheat?

My engine has been acting really funny lately, and i kinda cant really explain it, other than the fact that the passage was blocked.