wrote in message
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The impeller in a car waterpump is METAL, for openers. Outboard
waterpumps have to work in a very different environment, and so they
are made of flexible materials. They are in contact with the insides
of the pump housing to maintain a needed seal, and the material also
can crack due to plain old aging and loss of flexibility. An outboard
impeller can deteriorate from just age, without having any hours on
it. That's why 2 years is a good time for routinely changing them even
if they have very low hours on them. Likewise, an event where a lot of
sand or mud gets sucked into it, or it is allowed to run while dry
will cause an early death. Running dry ruins them almost instantly.

They aren't ****. They are designed for a different set of rules than
a car water pump. Boats are not automobiles, nor are they airplanes.

An impeller of the type commonly used on outboards and small marine engines
can have too much flexibility. The vanes need to be quite stiff as, after
they have been pushed inwards by the cam, it is their inherent stiffness
that allows them to spring back quickly and thereby suck in more water.
I found this out when an impeller that seemed nice and flexible would pump
just fine at slow revs but would cease to pump at higher revs because the
vanes were too flexible to recover in the time available. I changed it for a
stiffer one and problem disappeared. I have never known one to crack and
think they would have to be out of use for a long time before this happened.
Do not forget that there is always one vane bent inward when the engine is
not in use so it pays to turn the engine over occasionally to move the
impeller around a bit.
Running dry is certainly sudden death to them and so I like to smear the
impeller with soluble oil (hand cleaner) when first starting unprimed in the
spring.

"Edgar" wrote in message
...

wrote in message
...
The impeller in a car waterpump is METAL, for openers. Outboard
waterpumps have to work in a very different environment, and so they
are made of flexible materials. They are in contact with the insides
of the pump housing to maintain a needed seal, and the material also
can crack due to plain old aging and loss of flexibility. An outboard
impeller can deteriorate from just age, without having any hours on
it. That's why 2 years is a good time for routinely changing them even
if they have very low hours on them. Likewise, an event where a lot of
sand or mud gets sucked into it, or it is allowed to run while dry
will cause an early death. Running dry ruins them almost instantly.

They aren't ****. They are designed for a different set of rules than
a car water pump. Boats are not automobiles, nor are they airplanes.

An impeller of the type commonly used on outboards and small marine
engines can have too much flexibility. The vanes need to be quite stiff
as, after they have been pushed inwards by the cam, it is their inherent
stiffness that allows them to spring back quickly and thereby suck in more
water.
I found this out when an impeller that seemed nice and flexible would pump
just fine at slow revs but would cease to pump at higher revs because the
vanes were too flexible to recover in the time available. I changed it for
a stiffer one and problem disappeared. I have never known one to crack
and think they would have to be out of use for a long time before this
happened. Do not forget that there is always one vane bent inward when the
engine is not in use so it pays to turn the engine over occasionally to
move the impeller around a bit.
Running dry is certainly sudden death to them and so I like to smear the
impeller with soluble oil (hand cleaner) when first starting unprimed in
the spring.

Depends of the brand and model of the motor. I have a 2 HP Seagull that has
a rigid impeller that works by centrifugal force. It can be run dry without
damaging it because it doesn't rub on the housing like the rubber impellers
do. There is no bending, no binding and no reason to turn the engine once in
a while to keep one vane from bending and cracking. The Seagull is clearly
superior to any new Suzuki. It will live in the marine environment for 20-30
years no problem. The Suzuki might last ten years with meticulous care.

--
Gregory Hall

"Gregory Hall" wrote in message
...

Depends of the brand and model of the motor. I have a 2 HP Seagull that
has a rigid impeller that works by centrifugal force. It can be run dry
without damaging it because it doesn't rub on the housing like the rubber
impellers do. There is no bending, no binding and no reason to turn the
engine once in a while to keep one vane from bending and cracking. The
Seagull is clearly superior to any new Suzuki. It will live in the marine
environment for 20-30 years no problem. The Suzuki might last ten years
with meticulous care.

--
Gregory Hall

You are right about Seagulls. Apart from my little Yamaha I have a Seagull
Century Plus that I got new in 1954 and I will never part with it.
It is really useful to be able to run it up dry on the bench so that you are
sure all is in order before you take it to the boat and it has a large
propeller that will push my 15' 6" wooden dinghy up to hull speed.
It is heavy, noisy and oily but I know it will not stop running for anything
as long as you feed it clean fuel. If it should stop you can fix any likely
problem in the boat with just three simple tools.
"They don't make them like that any more!"