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a bit but should return to something close
to straight within a day—if not, you need to
replace the impeller. The ends of the blades
should be round and not worn flat. Flex the
blades and look closely where they meet at
the center—no cracks should be visible. And,
of course, no pieces of the impeller should
be missing. If the impeller passes all these in-
spections, the impeller remains serviceable.
If the impeller is broken or worn, you
will need to inspect the rest of the systemfor associated issues. If pieces of the im-
peller have broken off, you will need to
find them downstream as they will restrict
the flow of the seawater cooling loop. You
may find them lodged in the discharge
port at the pump, at the inlet side of the
heat exchanger, or at the fitting where the
raw water injects into the exhaust elbow.
If the ends of the impeller are shiny
or cracked and some vanes are missing, it
likely ran dry at some point. If the bladesare intact but have worn tips or imprints
from the cam, you might have a blockage
on the discharge side creating too much
back pressure. Look at the inlet side of the
heat exchanger for an accumulation of an-
ode pieces or impeller bits.
Finally, if the impeller vanes have
pieces missing from the middle of each
tip, you might have cavitation inside the
pump from too much vacuum on the suc-
tion side. Closely inspect the cam and
pump housing for pitting and check the
piping between the seawater strainer and
the pump for restrictions. If this problem
has happened more than once you might
have to increase the diameter of the inlet
pipe fittings and hose.
Once these inspections have been
completed, it’s time to insert the new im-
peller (or the existing impeller if you have
determined it is still serviceable). The re-
placement impeller should match the part
number for your pump and engine. Seawa-
ter pumps should use impellers made of