5/12/22
After being towed in to Deltaville, Dan from Zimmermans showed up at 7 am the next morning, changed the oil & filter and disassembled the water pump. Looking at the internal remnants of the pump, and consulting with other mechanics, a foresnsic timeline of destruction was guessed at.
The pump sucks sea water (from a hole in the bottom of the boat) and circulates it around the engine. The sea water cools the engine and leaves the boat through the exhaust. It appears that something blocked the sea water and prevented it from entering the pump. And so…the pump ran dry, which stopped the flow of cooling water, which cooked the impeller (and shredded it to the point that even seasoned mechanics said ”WOW”). The heat that resulted caused a bolt (that held the cam inside the pump) to fail. This bolt is an internal and integral part of the pump. When it failed, the internal pump parts came adrift and destroyed the water pump from the inside. This bolt can’t cost more than a few bucks but the damage done will cost about 2 grand.
The fix requires replacing the pump and then fishing out any remaining bits of impeller from the rest of the cooling system. Getting a new pump and accompanying gaskets took 7 days and a lot if conversation about the supply chain. Disassembly an diagnosis took a day. Reassembly and run-up tests took a morning.
The question remains…what caused the water pump to run dry? We will never know. Leaving Norfolk we ran through some browninsh water that appeared to be left by a departing Navy ship…maybe. The most common cause of this type of failure is running over a plastic bag that stops the cooling water from entering the boat…maybe. Marine growth inside the intake could also cause a blockage…maybe. We found no evidence of any of these problems so were going with the plastic bag snagged over the intake theory…Although, for the life of me, I can’t see how a bag could become snagged on the highly engineered, hydrodynamic, underwater grate that protects our cooling system by guarding against this exact occurrence. The mystery remains.
After a 9 night delay, we are ready to resume our adventure. Of special note is the kindness and hospitality extended to us by the Regatta Point Marina. Don, Nancy and Mike went out of their way to make sure that we had everything we needed, from bicycles to loaner cars to local guidance. Their graciousness made our stay enjoyable. Southern hospitality at its best!
Wow…yuck. Another possible version of the story is that the screw started unscrewing, chewing a groove into the middle of each blade, and eventually came out, at which point larger blade pieces got shed and eventually blocked the flow (as well as no longer producing any flow!). As I recall, the assembly instructions advise a little loctite on that screw. But as you say, it’ll probably remain a mystery.
Could have happened either way. The old pump was replaced 163 hours ago and the remains of the bolt were still in the housing, but the threaded part had a clear shear fracture. Glad to be up and running. Now in Solomons after a perfect 7 hour run up the Chesapeake!
John, the shank of the screw remained in the housing with a clear shear fracture on the inside surface. Will never know if this was a cause or effect of the problem.
Plastic bags are more of a problem with the lower unit on outboards,where they have something to wrap around. Maybe it was leeches blocking the intake (like the ones that attacked Bogey in the African Queen)LOL. Being out a little longer and having time to explore more is your consolation prize!
Ha ha Mike, the thought occurred to me that we had started growing oysters in the intake but a quick swim confirmed that nothing was in there.