Older Yanmar pumps have trouble keeping the pressure up to maintain
the flow unless the pump clearances are correct. This is more of a
problem on boats with hot water heaters, engine driven refrigeration
and water-lift exhausts.

When replacing the raw water pump impeller it is important to check
the clearance between the parting surface and the impeller. Make sure
the impeller is all the way in the pump then with a straight edge and
a feeler gauge check the free clearance of .001 to .002 of an inch. If
there are too gaskets on the pump plate instead of the thin one
supplied by Yanmar, pumping pressure will be effected.

On 2GM and 3GM engines that are salt water cooled a stuck closed or
missing thermostat will bypass the water all the time causing the
engine to overheat.

From the author of four books on boat refrigeration.
http://www.kollmann-marine.com

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

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

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/

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!!

On Sun, 04 Jan 2004 19:29:28 GMT, "Jeffrey P. Vasquez"
wrote:


"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!!


I had one impeller fail by the rubber coming adrift from the metal
bushing - everything looked fine, but the rubber didn't turn.




--
Peter Bennett, VE7CEI
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

On Sun, 04 Jan 2004 19:29:28 GMT, "Jeffrey P. Vasquez"
wrote:


"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!!


I had one impeller fail by the rubber coming adrift from the metal
bushing - everything looked fine, but the rubber didn't turn.




--
Peter Bennett, VE7CEI
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

"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!!