Hello all,

I recently did a standard maintenance replacement of a raw water impeller
on a Yanmar 2GM diesel. Everything seemed straightfoward, part for part,
no leakage, everything went back together straight away and test runs at
the dock were nominal.

However, during a move to a new slip the engine alarm went off. A
subsequent check revealed nothing. Took the boat out and ran the engine
for a good hour and there were no issues. The second time out the engine
alarm went off again after about the same duration of running time as the
incident during the move to the new slip.

This time there was no curing it. I dismantled everything upstream and
downstream of the water pump and it appears there is no flow through the
water pump even though everything appears to be functioning exactly as
it's supposed to. The impeller is fine, the belt tension and pulley
function are fine and there are no blockages from the through-hull to its
egress.

The boat is a 1989 S2.

I am stumped. Any suggestions would be infinitely appreciated.

Thanks,

"Jeffrey P. Vasquez" wrote in
message ...

This time there was no curing it. I dismantled everything upstream and
downstream of the water pump and it appears there is no flow through the
water pump even though everything appears to be functioning exactly as
it's supposed to. The impeller is fine, the belt tension and pulley
function are fine and there are no blockages from the through-hull to its
egress.

Egress from downstream of the pump? or to the pump inlet?

Now I don't know the details of your Yanmar, but here goes -

Where is your over-temperature sensor? In the fresh water system? Salt water
system or in the exhaust? That'll tell you quite a bit and may answer later
questions.

So, just to confirm, is salt water flowing from the exhaust/outlet when the
engine is running?

If in normal quantity, then there's likely to be a fresh water flow problem
(if the overheat sensor is in the fresh water system).

If reduced quantity, then there's likely to be a partial salt water blockage
which may not show up in a simple check, but which will effect cooling at
higher revs.

If no water, there's either a blockage which you haven't detected
(downstream of pump?) or the pump is not pumping.

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 . . .

Have fun. Maybe someone who knows your Yanmar will give you a better story.
--
JimB
Yacht Rapaz, sadly for sale:
http://homepage.ntlworld.com/jim.bae...cification.htm
jim(dot)baerselman(at)ntlworld(dot)com

"Jeffrey P. Vasquez" wrote in


This time there was no curing it. I dismantled everything upstream and
downstream of the water pump and it appears there is no flow through the
water pump even though everything appears to be functioning exactly as
it's supposed to. The impeller is fine, the belt tension and pulley
function are fine and there are no blockages from the through-hull to its
egress.

"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 . . .

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

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)

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]

On Sun, 04 Jan 2004 19:13:50 GMT, "Jeffrey P. Vasquez"
wrote:



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).

I may be misunderstanding you here. There is no difficulty telling
visually whether a yanmar is raw cooled or fresh. the heat exchanger
in the fresh-water-cooled engines is a rectangular tank above and to
the right of the cylinder head with a radiator cap in it. It has four
hoses, in and out for both raw and fresh water.

A raw cooled engine does not have this at all.




Rodney Myrvaagnes J36 Gjo/a


Does one child rape really change Strom Thurmond's lifetime record?
For better or worse?

Rodney wrote:
I may be misunderstanding you here. There is no difficulty telling
visually whether a yanmar is raw cooled or fresh. the heat exchanger
in the fresh-water-cooled engines is a rectangular tank above and to
the right of the cylinder head with a radiator cap in it. It has four
hoses, in and out for both raw and fresh water.

A raw cooled engine does not have this at all.

Yes, it's raw. I always leave the door open to be enlightened when I know I
am not an expert.

Rodney wrote:
I may be misunderstanding you here. There is no difficulty telling
visually whether a yanmar is raw cooled or fresh. the heat exchanger
in the fresh-water-cooled engines is a rectangular tank above and to
the right of the cylinder head with a radiator cap in it. It has four
hoses, in and out for both raw and fresh water.

A raw cooled engine does not have this at all.

Yes, it's raw. I always leave the door open to be enlightened when I know I
am not an expert.

On Sun, 04 Jan 2004 19:13:50 GMT, "Jeffrey P. Vasquez"
wrote:



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).

I may be misunderstanding you here. There is no difficulty telling
visually whether a yanmar is raw cooled or fresh. the heat exchanger
in the fresh-water-cooled engines is a rectangular tank above and to
the right of the cylinder head with a radiator cap in it. It has four
hoses, in and out for both raw and fresh water.

A raw cooled engine does not have this at all.




Rodney Myrvaagnes J36 Gjo/a


Does one child rape really change Strom Thurmond's lifetime record?
For better or worse?

"Jeffrey P. Vasquez" wrote in
message . 17...


Your diagnositcs seem to point clearly at a pump issue. More further on -

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?

Possibly.

You didn't mention removing the cam, so I'm assuming that's still in place.

Depends on your gasket thickness, the length of your replacement
impeller, and how stiff it is on the shaft.

Too long an impeller, or too thin a gasket (or both!) can cause
the impeller ends to seize against the cover plate once the cover is
tightened up. At the next start, the shear occurs.

Also, if the impeller is a very tight fit on the shaft, it may be pushed in
too hard and jammed against the back plate, or it may be standing a little
too proud and jamming against the front plate. At the next start . . .

Missing out a gasket obviously also has the same effect.

With a raw water only system you'd overheat pretty quickly. Your test
separating the pipe at the engine block and seeing no water entering the
block eliminates the most common blockage problem, which is the slow build
up of calcium and borate salts in that areas which regularly cycle through
hot and cold. Also, this type of build up is over the years, not days!

Sorry you're not having fun! Barked knuckles, hacksaw mashed screw slots,
lost screws in the bilge drains and used diesel oil deodorant and finger
colouring does all seem to be all part of the game. No wonder my wife tells
me not to hand the bread to our visitors!


I have read that water flows through the water pump without rotation of
the impeller.

Not significantly. You'll get a drip rate around the backplate and endplate
if there's a positive pressure, more with wear. Any more and the gasket's
too thick or the impeller too short (opposite to the seizure problem). This
leakage is trivial compared to the pumping capacity of the vanes.
--
JimB
Yacht Rapaz, sadly for sale:
http://homepage.ntlworld.com/jim.bae...cification.htm
jim(dot)baerselman(at)ntlworld(dot)com

"Jeffrey P. Vasquez" wrote in
message . 17...


Your diagnositcs seem to point clearly at a pump issue. More further on -

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?

Possibly.

You didn't mention removing the cam, so I'm assuming that's still in place.

Depends on your gasket thickness, the length of your replacement
impeller, and how stiff it is on the shaft.

Too long an impeller, or too thin a gasket (or both!) can cause
the impeller ends to seize against the cover plate once the cover is
tightened up. At the next start, the shear occurs.

Also, if the impeller is a very tight fit on the shaft, it may be pushed in
too hard and jammed against the back plate, or it may be standing a little
too proud and jamming against the front plate. At the next start . . .

Missing out a gasket obviously also has the same effect.

With a raw water only system you'd overheat pretty quickly. Your test
separating the pipe at the engine block and seeing no water entering the
block eliminates the most common blockage problem, which is the slow build
up of calcium and borate salts in that areas which regularly cycle through
hot and cold. Also, this type of build up is over the years, not days!

Sorry you're not having fun! Barked knuckles, hacksaw mashed screw slots,
lost screws in the bilge drains and used diesel oil deodorant and finger
colouring does all seem to be all part of the game. No wonder my wife tells
me not to hand the bread to our visitors!


I have read that water flows through the water pump without rotation of
the impeller.

Not significantly. You'll get a drip rate around the backplate and endplate
if there's a positive pressure, more with wear. Any more and the gasket's
too thick or the impeller too short (opposite to the seizure problem). This
leakage is trivial compared to the pumping capacity of the vanes.
--
JimB
Yacht Rapaz, sadly for sale:
http://homepage.ntlworld.com/jim.bae...cification.htm
jim(dot)baerselman(at)ntlworld(dot)com