gonzo...need some help quick

[zr1_lt5]

hey gonzo (and anyone else who can answer this) i got a question that i need an answer for pretty soon... a little while ago you helped me figure out that my cooling problems were being caused by clogged water passages in the exhaust manifolds...i cleaned them out partway, and it cooled fine for a while...but apparently i didnt clean them out well enough because it is now overheating again....the question is....are you absolutely sure that it is possible to clean them out thoroughly? and if so, how do i do this? I need to know this because i took my boat to a mechanic yesterday, and he is now telling me that he has to replace the manifolds (at a cost of $1000) before he can start diagnosing other problems with the engine. he told me that it is impossible to clean the clogged manifolds and that they have to be replaced.
please help, because i would like to get an answer to him before he closes for the day. (4:30 or so)

[woodboat]

It is also very common to clog the water passages in the block. If this is a small chevy to my knowledge the only way to clean the block is with heads removed. What were the manifolds clgged with? If mud and sand then yes they are easily cleaned.

[zr1_lt5]

i am positive it is the manifolds...we have tested the block and it flows fine...they are getting clogged with carbon from the exhaust

[gonzo]

If it is only carbon, cleaning them shouldn't be too difficult. If they have scale rust, they may have to be changed. When the corrosion is severe, even if you manage to clean them, the manifolds will end up cracking or with pinholes that will leak water internally.