[Rhodes22-list] Yamaha 9.9 Water Pump Replacement

[Roger Pihlaja]

Jay,

The usual problem with the water pump impellors on small outboards is that
they are made from some sort of rubber.  It's really a rather clever design.
At low speed & at start-up, the rubber vanes on the impellor touch the water
pump housing, thus making the pump positive displacement & self-priming.  At
high speed, the rubber vanes deflect out of the way & ride on top of a
boundary layer of water on the wetted surface of the water pump housing.  At
high speed, the vanes don't experience any wear because they are not
touching the pump housing.  This design makes the water pump capable of
automatically switching from positive displacement mode to centrifugal mode
for delivering the high volume of cooling water required by high speed
operation.

So what goes wrong?  Well, if the water pump ever runs dry, the rubber
impellor will lose the lubrication & cooling provided by the water,
overheat, & destroy itself very quickly, like in a few seconds!  Exposure to
oil & gasoline in the water (like the oil film that laid down by 2-cycle
outboards) will gradually break down the rubber polymer molecules in the
impellor; leading to embrittlement, cracking, and failure.  This is probably
the single biggest long-term failure mechanism.  Pump impellors should be
routinely replaced every 4 years due to this cause alone.  There is also
another common failure mechanism related to storage.  When the lower leg is
lifted free of the water, the entire cooling system drains down.  This is
why the water pump needs to be self-priming at start-up.  Even fresh water &
especially ocean water, has a certain amount of dissolved mineral salts in
it.  When the cooling system drains down, a small amount of water is left
trapped in between the ends of the vanes on the water pump impellor & the
aluminum pump housing.  When this water eventually evaporates in storage,
the impellor vanes can be bonded by salt crystals to the pump housing.
Depending upon how strong this bond is, the rubber impellor can be damaged
the next time the engine is started when the vanes are ripped free of the
salt crystals.  In addition, for the 1st few minutes of operation, before
the salt crystals dissolve, they form a relatively rough surface on the
water pump housing that the rubber vanes have to run over on every
revolution.  Finally, there can be corrosion issues with moist salt crystals
in long-term contact with the aluminum pump housing in this scenario.  In
salt water, it's considered good practice to fresh water flush the cooling
system after every use & certainly before long-term storage.  After
long-term storage, it wouldn't hurt to fresh water flush the cooling system
prior to start-up.  As part of my outboard winterizing proceedure, I flush
propylene gylcol potable antifreeze (RV "red pop") thru the cooling systems
of my outboards.  propylene glycol will prevent the build-up of salt
crystals in-between the vanes and the water pump housing.  During the
boating season, on every start-up, I gently pull the outboard thru with the
pull cord prior to starting it to break the water pump impellor free & give
the engine several minutes of low speed warm-up.

The result, the only water pump I've ever had fail on any of my outboards in
25+ years of boating was the time when my younger son Gary ran the
inflatable dingy & Honda 9.9 hp outboard up on the beach with the engine at
full throttle.  The water pump impellor was burnt to a crisp!

Good luck!

Roger Pihlaja
S/V Dynamic Equilibrium
----- Original Message -----
From: "Michael Meltzer" <mjm at michaelmeltzer.com>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Wednesday, February 11, 2004 2:25 AM
Subject: Re: [Rhodes22-list] Yamaha 9.9 Water Pump Replacement


> sounds like overkill and make work, maybe the impeller very 4 years, but
the complete pump, nah. you are only putting 25-50 hours on
> the motor every year, one thing you do have to watch is salt on the
thermostat(and blow the pelages, clean the pee tub yearly), is
> one of the few parts on the engine that is not rust proof, time will get
it and they need to be replace every two years, luckily it
> is also a simple job that you can do yourself.
>
> MJM
>
> ----- Original Message -----
> From: "Jay Friedland" <a.jayf at verizon.net>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Tuesday, February 10, 2004 11:25 AM
> Subject: [Rhodes22-list] Yamaha 9.9 Water Pump Replacement
>
>
> > Folks,
> > My ob service guy says Yam recommends replacing the water pump assembly
> > every year. The motor is 2001 with this the first year in service. I'm
> > in salt water 9-10 months, occasionally flush with ear muffs (once a
> > month), and end of season run it in a barrel of fresh water for 1/2
> > hour (alos to burn off deposits, etc.).
> >
> > Anybody offer best suggestions on proceeding with this replacement or
> > any other winter routine?
> >   Thanks, Jay
> >
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> >
> >
>
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