"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)

"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.