Yanmar 1GM User Manual page 177

Impeller
direction
8
COOL ING SYSTEM
Seawater Pump Precautions
The seawater pump suffers from many misconceptions
about its ability to withstand operation without water be-
ing supplied to it. All impellers are made of some varia-
tion of rubbe r. The water pump housing is made of metal.
If a piece of rubber is rubbed across a piece of metal, there
is severe friction and considerable heat buildup. However,
if the metal is flooded with water while the rubber is
moved across it; the friction would be greatly reduced and
the heat bui ldup non-existent.
Basically, the water pump works the same way. The wa-
ter passing through the pump lubricates and coo ls the im-
peller and pump housing. Without the water, the pump
will overheat and the impeller
will
begin to melt almost
instantaneously. Of course, this can be secondary to the
potential damage to the engine from overheating.
Once the impeller sustains any damage, its pumping
ability is greatly diminished because the impeller can no
longer seal adequately. The impeller must seal on its
edges, as well as the blade tips.
171
Ifthe engi ne was run without an adequate supply ofwa-
ter to the pump, disassemble the pump and replace the im-
peller and any other damaged parts.
Water Pump Operating Mtsrakes
Do not run an engine immediately after pulling a boat
out of water. This is an extremely risky operation, but here
is why some peop le often seem to get away
with it. If
an
engine has j ust been pulled out of the water, there is resid-
ual water in the cooling syste m and engine that dra ins
back down to the wate r pump. This water will lubr icate
the water pump for a short perio d of time (perhaps a cou-
p le of minutes), but the pump will be damaged as soon as
the heat from operation evapo rates all water in the system.
Do not operate the pump without an adequate water sup-
ply. ....-.....,
Do not stan an engine with the boa t out of the wa ter, but
without a water supply, to ma ke sure the motor will run
1. ..1
when the boat is launched. This is an unacceptable and
very dangerous procedure . If an engine has been sitting
for any length of time, the water pump is completely dry
and the impeller will sustain immediate damage if the en-
gine is operated without an adequate water supp ly. Water
must be supp lied to the pump through the boa t's water in-
take or supplied under pressure from a flushing device .
CAUTION
Supply the pump with an adequate water
supp ly anytime the engine is running.
Do not cran k the engine for an extended period, such as
during troub leshooting. This is detr iment al to a water
pump that is completely dry. Consi der attaching a flush-
ing dev ice before initially cranking an engine with a dry
wate r pump. This will ensure the pump is wet and will not
be damaged.
It
will not be necessary to keep the water
supply flowi ng during all cranking
periods; it is just im-
portant to keep the pump wet during extended cranking.
Removal/Installation
I GM and I GMIO
I. Ifthe boat is in water, make sure the seacock is closed.
2. Drain the seawater from the engine as described in
Chapter Four.
3. Loosen the hose clamps, then detach the water hoses
from the sea water pump.
4. Remove the pump retaining screws (F igu re 21) and re-
move the pump. Remove and discard the gasket, if so