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.

"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

another problem I have seen on yanmar model 2qm15 is that the Zinc
mounting housing (Salt/raw water cooled) has the hose from the water
pump to the zinc housing mounted in a verticle orientation with the hose
from water pump to zinc housing coming from underneath the zincs house.
When replacing the original hoses I found the zinc had built up a crust
inside the hose under the zinc housing to the point where the hose was
becoming constricted by the build up, might as well replace your zincs
and check for that .

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

Yes, it's raw.

another problem I have seen on yanmar model 2qm15 is that the Zinc
mounting housing (Salt/raw water cooled) has the hose from the water
pump to the zinc housing mounted in a verticle orientation with the hose
from water pump to zinc housing coming from underneath the zincs house.
When replacing the original hoses I found the zinc had built up a crust
inside the hose under the zinc housing to the point where the hose was
becoming constricted by the build up, might as well replace your zincs
and check for that .

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

Yes, it's raw.

I've had the same problems with my water pump on my 2GM and three different engineers have thought that the hoses had delaminated, the anti syphon valve had failed or the thermostat had seized. All things that I'd checked anyhow.
It runs from cold for as long as I want pumping water from the back but as soon as I shut it down, sail for a bit and then start it up the pump fails.
My thinking was this - the cam and inside face of the pump have worn enough from sand/silt that a warm engine creates a pressure differential in the cooling system to prevent a failing/failed pump to pump - but running from cold the cooling system, once pumping, will syphon.
However, the notion of the pulley spinning on the spindle (above) also works in my mind, i.e. the pump works and syphons from cold but a hot (and expanded) pulley will not pump although visually all looks good.
I'll check the pulley at the weekend but regardless I'm buying a new pump.
But, here's the thing. A replacement raw pump - about 40 litres a minute costs £366 but a freshwater pump (exactly the same mounts but a bigger impeller) costs £120 and pumps around 50 litres a minute.
I'm sure that the thermostat will regulate the flow through the engine anyway, but has anybody got any experience of increasing the flow in this way? I spoke to Yanmar UK and they told me to fit the raw water pump but had no advice regarding the freshwater pump.