Cooling System Repair Tips
systems in general are quite reliable. As the size of the motor
increases however the complexity also increases and you must check
all the components for proper functionality. To and including temperature
sensors, thermostat(s), pressure relief/bypass valves, overboard
hoses and fittings.
Cooling system and waterpump ills can be alleviated by replacing the pump every so often. Impellers take a set when unused and can shed vanes fast when you operate the outboard after an extended period of storage. I advise that ANY motor which has been idle for more than 1 year have a VISUAL check of the pump. It's real easy to install a new impeller and avoid extensive engine damage caused by an overheat.
Run your motor without water, and the impeller
and housings on a modern outboard will be ground into scrap in
30 seconds or less!
START THE MOTOR ON THE TRAILER WITHOUT WATER TO THE ENGINE !!
Should you find that the pump has self-destructed
due to lack of water, be VERY CAREFUL to be certain that fragments
of the impeller have not passed into water tube and block and restricted
passages. If you suspect that you have not recovered all of this
material, better safe than sorry and remove ALL the covers and clean
IF your motor has suffered a cooling system
failure, there are several factors to consider depending on the
severity. You MUST replace the head gasket as overheating will turn
it into carbon and its sealing properties will be destroyed. Check
the exhaust cover gaskets as well. Motors equipped with thermostats,
will generally require replacement of the stat as well as the pressure
relief bypass valve, a plastic part that will likely be melted.
A severe overheating could have damaged the pistons and rings. If
removal of the head shows any parallel vertical lines in the cylinders,
or worse yet, aluminum transfer to the walls you should remove the
transfer covers and the exhaust plate to check the pistons for scuffing.
Many times transferred aluminum can be removed
from the cylinder walls with Muriatic acid. Observe common sense
precautions when using this strong acid! CAREFULLY, using a cotton
swab, apply only to the affected area until it stops fizzing, the
aluminum deposits will be eaten away. You must thoroughly neutralize
the acid with soda after cleaning off the aluminum! A light scuffing
up to remove embedded carbon and restore some crosshatch with some
oiled 320 grit wet-or-dry sandpaper will heal up a slightly scuffed
To help the motor heal itself from the
distortions caused by an overheat, I recommend you run it on a 24:1
oil mixture for several hours as well as limiting the speed to 1/2
throttle or less. When you finish initial testing on an overheated
engine, be sure to retorque the fasteners on all covers removed
to check it over as well as retorquing the head gasket.
IF you wish to service or repair your
own cooling system, I HIGHLY RECOMMEND you obtain an OEM model-specific
service manual to help you. We have most available Right
Here at Mastertech.
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