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thoughts on how to clear rust blockage in v8 coolant chamber?

stang32

Regular Contributor
i am working on a 7.4 merc. and the port side plug was solidly blocked with scale. i cleared it out as best as i could go without knocking out an expansion plug. i pressurized the system by plugging all the exit hoses and sending water pressure in via a garden hose but got just a trickle of water out. no voluum at all. i am planning to bring an air compressor to the boat and sending forced air into the 1/4" plug opening. anyone ever have a case like this? if this doesnt work, i will knock out the expansion plugs and go that route.
 
Have used the air route when wire and flex cable didnt do the job.And knocking out a plug or two is the only other option short of stripping the block and having it tanked.
Guessing this was run thru a lot of silt and sand and never had the plugs removed for winterizing?
 
Have used the air route when wire and flex cable didnt do the job.And knocking out a plug or two is the only other option short of stripping the block and having it tanked.
Guessing this was run thru a lot of silt and sand and never had the plugs removed for winterizing?

yeah, i dont know what the PO did or how this engine didnt crack already due to poor winterization. he must have been pretty lucky
 
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