The failure of a simple rubber impeller
can spoil a planned weekend on the water. That’s why any well-equipped boat will
have spares aboard. While you can’t have spares aboard for everything, you can have
spares for a few of the most likely items to fail and impellers are high on the
list. You might have as many as seven or more of them here and there on your boat.
Your boat has pumps all over it and most use impellers – which can fail for
several reasons at any time.
Courtesy of Virtualboatyard.com--
Ever stop to think how dependent your boat is on a little rubber impeller? Or how
many of them you have aboard? Depending on the size of your boat, it could be from
one to as many as seven or more. They reside in your outdrive, electric head, pressure
water system, wash down pump and oil change system, engine cooling water pump, and
fuel pump for example. Failure of any of them could result in consequences that
range from a smelly mess, a delayed vacation, to a possible sinking or expensive
damage to your engine and drive train.
Two basic impeller types.
Some manufacturers recommend replacing the impeller every year. Some OEMs recommend
removing the impeller from its housing during winter lay-up. Most of us don’t do
Impeller pumps generally fail in one of two ways. The first is a gradual degradation
in pump performance and flow. This is usually due to impeller or housing wear or
The second failure mode is sudden, catastrophic failure, with the impeller usually
loosing some or all of its blades. This is usually caused by running the impeller
pump dry. Remember, the fluid being pumped provides the cooling and lubrication
for the pump. This is often caused by a water inlet seacock not being opened or
a plastic bag covering the water inlet.
The impeller often sheds its blades in such a failure. The errant blades must be
tracked down and removed from the system, especially if it is an engine cooling
application. Failing to do so will usually lead to further problems and blockages
Outboard Motor Pumps…
Typical outboard motor water pump housing with stamped steel liner.
Outboard engine pumps are probably the most difficult to maintain. Changing the
impeller requires separating the lower gear case from the engine. This also may
require disconnecting the shift linkage. Consult your engine manual for the specific
steps required the get to the pump.
When the lower unit is free, the pump will usually be located on top of the gear
case. The housing can then be unbolted and the impeller replaced. Carefully inspect
the housing and the stamped steel liner for signs of wear or overheating. Rebuild
kits are available that range from just the impeller and gasket, to kits that include
upper and lower housing as well as the wear plate. If in doubt, replace. You don’t
want to have to drop the gear case any more than necessary.
Engine Cooling Pumps…
Most engine cooling pumps have a cover plate held on with several screws. Removing
the screws and cover plate exposes the impeller. If the impeller has been changed
regularly, it should just slide off the shaft. In many cases, it will need to be
pried out with a couple of screwdrivers. Take great care not to damage the housing,
these can be expensive to replace.
Engine driven cooling water impeller pump.
Many manufacturers make impeller puller, much like gear puller, for extreme cases
but they are pricey. Some manufacturers have threaded the inside of the exposed
end of the impeller. Removing this type of impeller is a simple matter of threading
the right size bolt in the open end. As the bolt is tightened, it bears on the pump
shaft and backs the impeller out. More manufacturers should consider this design
Freestanding impeller pumps are usually easy to disassemble and service, if the
pump itself is accessible. A hint when servicing a macerator pump: place plenty
of adult diapers around and under the pump to soak up any “stuff” that may dribble
out of the pump.
Do Your Homework First…
Before you decide to perform maintenance on your impeller pump, take a few preliminary
steps. Make sure you have identified the exact pump you have and have the appropriate
rebuild kits or replacement impellers on hand. There are several pump and impeller
manufacturers and many make interchangeable impellers. Have all those numbers available
when you shop for spare parts. Your store may carry only one brand or the other
(you DID document those numbers in your onboard maintenance manual, didn’t you?).
Impeller Pump rebuild kit (Typ.)
Make sure the right tools are available. Do a dry run to make sure the tools fit
the jib. Special wrenches or short screwdrivers might be required. Trying to replace
an impeller at night on a rolling sea isn’t the time to develop your repair strategy.
Impeller pump maintenance isn’t rocket science and is well within most boat owner’s
capabilities. Make sure you have the parts and tools before starting and don’t be
afraid to look at the service manual or rebuild kit directions.
--Capt’n Pauley, Virtualboatyard.com