First things first: Jim, Roy and all who responded, thank you! To receive
such a wealth of useful information in such a short amount of time goes
so far in reducing the frustration from this issue that I can't thank
everyone enough.

You're all tops in my book and usenet continues to rule!

Now, back to my regularly scheduled issue...

"JimB" wrote in message news:...
snip
You can check most pumps by taking the cover off and turning the
engine over with the starter while holding the fuel cut-off. If the
vanes don't turn, there's a shear failure somewhere or a missing key,
and that's your problem. If they do turn - your pump is almost
certainly OK. Back to the partial blockage . . .

Additional information: (everything Roy says I experienced is exactly
what I experienced, but I'm going to throw in my diagnostics before I get
into that and maybe someone can teach me something about my clinical
method as well). I disconnected the raw water ingress into the water pump
and sea water flowed freely from the hose (after turning on the through-
hull valve). After reconnecting that, I disconnected the hose leading
from the egress of the water pump to the engine block, aimed it at the
bilge and started the motor...nothing coming out. That seemed pretty
definitive to me. (I've left out steps starting with the strainer and all
points in between and skipped to the stuff which I think was clear cut
and supports Roy's analysis).

Btw, I still haven't found the heat sensor; the Yanmar book isn't
particularly clear on some details, I haven't downloaded the S2 manual
PDF yet, etc., but the engine is definitely hot. And it's raw water, not
fresh water (as I understand it).

Have fun. Maybe someone who knows your Yanmar will give you a better
story.

Fun I did not have. Vessel Assist I did have. =)


(Roy G. Biv) wrote:
I had a VERY frustrating overheating problem, sounds VERY similar to
what Jeff describes and Jim has Almost focused on what the problem
was . For me it was very frustrating, check strainer, check hoses,
check impeller, (still overheats) check pump (ok), pull exhaust
(still overheats), replace w new impeller (still overheats) put in 2nd
new impeller (still overheats) damn thing would run FINE at idle in
the canal, when I get out the channel and pick up rpm it would
overheat., seastrainer clear from beginning, no air leaks.

take pump cover off, R&R impeller & never find anything wrong. Put it
back together and runs fine at idle. (sound familiar Jeff?)

Finally I discovered what was happening was what Jim alluded to -- a
shear failure. Where the pulley fits on the water pump shaft was the
problem. There was enough drag to (pump off engine) to turn the pulley
by hand and observe the shaft spin & impeller turn (offering NO CLUE
because it APPEARED to be OK). Under load the drag was overcome and
EVEN THOUGH I could see the belt spinning the pulley, the drag on the
impeller overcame the shaft/pulley drag .

The problem was Both the pulley and the shaft, couldn't just relace
the pulley had to replace the shaft, to replace the shaft needed new
bearings and seals & by the time you add the shaft, bearings, seals, &
pulley together as a parts order it made more sense (cents!) to just
buy a new pump assembly (not cheap either)

Okay, not just *very* familiar, but spot on exact. However, if I am
understanding your description, it seems you were in the act of
rebuilding or partially rebuilding the water pump prior to the fault? Is
it possible that simply opening the back plate, removing the worn
impeller (worn, but no missing vanes), installing a new impeller,
replacing the gasket and replacing the backplate could result in the
sudden occurrence of this shear issue? Could the friction generated by
the fresh rubber of the new impeller (and possible dry running, though
the engine manual says dry-running will destroy the impeller in seconds,
which it didn't or wasn't) have caused a shear issue between pulley and
shaft where none existed before?

I have read that water flows through the water pump without rotation of
the impeller. I note that in my case there is no positive seal within the
water pump housing and impeller, is this correct? It seems
counterintuitive to me with the whole function of the rubber vanes and
the cam within the pump, so maybe I'm just having trouble grasping its
operation.

There is some slight scoring on the backplate, but it's extremely
minimal. If there's no positive seal within the pumping mechanism, what
does the scoring affect, other than friction?

I think I've bypassed the issue of plugged outlet downstream from the
pump (though there is so much downstream of the pump I am confident there
will be plenty of opportunity for the suggested blockage to happen in the
near future) by disconnecting the feed directly from the water pump and
into the engine block and running the engine. Is it possible this is not
as well-defined as I'm leading myself to believe?

Again, thank you all! This was demoralizing to have what seems such a
minor piece of hardware and rudimentary technology present such a huge
issue and it was very heartening to hear Roy's story on how pernicious
the issue could really be.

Deepest regards,

[Cool sailing-related .sig here when I are a real sailor]