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

On Sun, 04 Jan 2004 09:35:34 GMT, "Jeffrey P. Vasquez"
wrote this crap:

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.

Was there water coming out the water exit while the motor was running?




This signature is now the ultimate power in the universe

While it has never happened to me I have heard the hoses to the pump can
delaminate. They will look normal on the outside but the inner rubber has
separated from the outer and is drawn in by the flow. When drawn in it
restricts the flow and causes a vacuum which causes more hose to plug.
Sometimes the entire hose is sucked it which is a dead give away.

"Horvath" wrote in message
...
On Sun, 04 Jan 2004 09:35:34 GMT, "Jeffrey P. Vasquez"
wrote this crap:

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.

Was there water coming out the water exit while the motor was running?




This signature is now the ultimate power in the universe

"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)

"JimB" wrote in message ...
"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.

Had nearly the same problem on a used 2GM I installed on my 28' S2.
The problem was downstream of the water pump at the outlet of the
cooling jacket. Salt and corrosion had built up to stop the flow. It
took some time to remove the corrosion and salt but it now flows fine.
It has been a couple of weeks since I looked at the engine so I do
not recall the layout.

David OHara
"Ragtime"

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

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 . . .

jUST adding a little, Did you replace the wear plate on your pump? Is
it a jabsco? If it is a jabsco and you did not replace the wear plate
that might be a good place to start. Are you getting the same amount
of water out of your exhaust? If so than its you fresh water pump, or
like jeffery said perhaps your heat exchanger is clogged up.


Good luck

Joe

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

In article ,
"Jeffrey P. Vasquez"
wrote:

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.

Try the impeller you took out -- it sounds like it was working before.
Happened to us once. We got just enough flow for idle power.

After that, I'd dismount the pump, leaving the input hose on, put the
output into a bucket and power it with a drill. If you get good output,
then it's downstream.

We also found out that we have about 5 minutes' cruise power with no raw
water flow: Takes that long for the fresh water loop to get hot.
Probably takes longer if you have a domestic hot water tank in the loop.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Check your hoses and a part of the pump housing I believe is called the
impeller cam. It is the piece that makes the impeller deform to cause the
water to travel down stream rather than possibly stall within the pump. It
is a replaceable part and one often overlooked.
"Jeffrey P. Vasquez" wrote in
message ...
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,

"The Carrolls" wrote:
Check your hoses and a part of the pump housing I believe is called
the impeller cam. It is the piece that makes the impeller deform to
cause the water to travel down stream rather than possibly stall
within the pump. It is a replaceable part and one often overlooked.

Thanks Jere and the Carrolls! It is profoundly encouraging to have such
quick and helpful responses. My thanks.

[This was cross-posted to rec.boats.cruising and a fellow usenetter there
wrote up an extremely good summary of shaft/pulley shear resulting in
exactly these symptoms, if you'd like to hop over there and read it.]

Thanks again!!