Impellers do fail. I was sitting at the quay in Papeete happily recharging batteries with engine running. (1977). Guy walks down the quay and says " no water
coming out, mate". He helped me change the impeller--no damage done. It was one of those English
engines we had in that boat. (Perkins?) No idea of impeller make.
Fastforward 2009. 2,000 miles offshore
Chile-Gambier and I start engine after 2 weeks of battery charging
magic. No water
coming out exhaust
. I start at sea water through hull
and check everything downstream. No garbage bags clogging, all hoses attached properly, all looking normal. Must be impeller. Change impeller. (not easy on my boat. Yanmar
has impeller housing mounted facing aft so I must use mirror for everything). Not worried, I was a dentist before I started changing impellers and have always done everything backwards. Had no impeller-puller so used 2 screwdrivers to pry out impeller. The impeller looked great when I got it out except for the scars left by steel
screwdrivers on rubber. Pitched impeller overboard
, installed new one and water flow was normal.
Happened twice afterward and I came to realize I had an air lock problem. Only after rough seas and no engine run for days. Undoing the sea water (Groco) strainer released the 'lock' and all goes well after that simple operation. Why do 'air locks' occur? Don't know, don't care. Know how to check it and release air block/lock.
I change impeller when it's convenient (on the hard) and watch water outflow from exhaust/water port carefully at each engine startup.
I have since purchased and impeller puller and have a box full of impellers. I do use an infrared temp gun on all main engine parts