Did you replace the hose from the water pump to the Zinc Housing?

water flow from the water pump on my 15 arrives at the zinc housing in
a vertical orientation, I found as the zinc dissolves a crust would
build around the bottom inlet of the zinc housing at the housing/hose
junction restricting flow......










"Jeffrey P. Vasquez" wrote in message 6...
Hello all,

It's me again and I've a new riddle to pose to you. It's the S2 with the
raw-water cooled Yanmar in a marine environment again. Here's the latest:

1) Through-hull has been thoroughly cleaned.
2) Raw water strainer and hoses have been replaced.
3) Water pump has been replaced.
4) Thermostat has been replaced.
5) Mixing elbow has been replaced.
6) Entire system has been "Marsolved" (marine solvent)

Here are the symptoms:

When the engine is first started there is a good flow of water through
the system as evidenced from the exhaust. The engine runs to temperature
(150F) and operates fine indefinitely with no fluctuation in temperature
at operating rpm.

After operating at temperature for some fifteen minutes (arbitrary, but
approximately the time it takes to clear the marina and channel), the
engine is stopped and allowed to cool. After cooling the engine is
restarted and no flow of water is observed as evidenced by the exhaust.
Running at idle or at operating rpm does not alter the condition and the
engine heats to alarm. This has been confirmed in absence of sailing,
i.e. a siphon break was suspected (and may have been a past culprit), so
the hoses were rerouted to ensure positive pressure to the water pump
when the boat is level.

If the system is disassembled upstream to downstream (after cooling
sufficient to touch), flow through it at all points is observed. If the
system is reassembled it will at this point again function properly.

I would liken this behavior to vapor lock in automobile fuel systems, but
I have no understanding how this would be relevant to the Yanmar cooling
system.

The mechanic's diagnosis is blockage in the engine block itself and the
suggested recommendation is replace the entire engine.

Any opinions, experience, recommendations or wild-eyed guesses would be
infinitely appreciated as always. If engine replacement is the correct
course of action, what does one do with a Yanmar 2GM with about 1800
hours and a suspected cooling blockage?

Many thanks!

The older Yanmar seawater cooled (raw water) pumps were not very
efficient and could not maintain water flow in a warm engine if any
air bubbles entered the pump. After replacing the cam in the water
pump every 500 hours and the impeller every 100 hours at 6000 hours I
solved the problem by installing an air bleed tube ahead of the pump.
If water is present in the exhaust when running at the dock and it
stops after a while when running under power, then it is a good sign
that the combination of heat and exhaust pressure from the water lift
muffler are preventing the pump from passing small amounts of air.
These are a few of the things done in the ten years I tried to solve
the problem; Moved through hull lower in the keel. lowered the water
strainer below the water line, installed a forward facing scoop on the
through hull, Removed the cylinder head and dissembled the exhaust
heat exchanger, and installed a early warming horn set to sound at 145
degrees exit water temperature.

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

(Roy G. Biv) wrote in message . com...
Did you replace the hose from the water pump to the Zinc Housing?

water flow from the water pump on my 15 arrives at the zinc housing in
a vertical orientation, I found as the zinc dissolves a crust would
build around the bottom inlet of the zinc housing at the housing/hose
junction restricting flow......










"Jeffrey P. Vasquez" wrote in message 6...
Hello all,

It's me again and I've a new riddle to pose to you. It's the S2 with the
raw-water cooled Yanmar in a marine environment again. Here's the latest:

1) Through-hull has been thoroughly cleaned.
2) Raw water strainer and hoses have been replaced.
3) Water pump has been replaced.
4) Thermostat has been replaced.
5) Mixing elbow has been replaced.
6) Entire system has been "Marsolved" (marine solvent)

Here are the symptoms:

When the engine is first started there is a good flow of water through
the system as evidenced from the exhaust. The engine runs to temperature
(150F) and operates fine indefinitely with no fluctuation in temperature
at operating rpm.

After operating at temperature for some fifteen minutes (arbitrary, but
approximately the time it takes to clear the marina and channel), the
engine is stopped and allowed to cool. After cooling the engine is
restarted and no flow of water is observed as evidenced by the exhaust.
Running at idle or at operating rpm does not alter the condition and the
engine heats to alarm. This has been confirmed in absence of sailing,
i.e. a siphon break was suspected (and may have been a past culprit), so
the hoses were rerouted to ensure positive pressure to the water pump
when the boat is level.

If the system is disassembled upstream to downstream (after cooling
sufficient to touch), flow through it at all points is observed. If the
system is reassembled it will at this point again function properly.

I would liken this behavior to vapor lock in automobile fuel systems, but
I have no understanding how this would be relevant to the Yanmar cooling
system.

The mechanic's diagnosis is blockage in the engine block itself and the
suggested recommendation is replace the entire engine.

Any opinions, experience, recommendations or wild-eyed guesses would be
infinitely appreciated as always. If engine replacement is the correct
course of action, what does one do with a Yanmar 2GM with about 1800
hours and a suspected cooling blockage?

Many thanks!


I had this same problem on my 2GM on my 8.5M S2 and the problem was
corrosion build up. Here is what you do:

1. Ignore that idiot mechanic.

2. Get the engine service manual so you can trace the raw water
coolant path. It isn't obvious so get the manual. You could try
Mastry Marine in St. Petersburg, Fl to get it where I got mine.

3. Get a 5 gal bucket, get some clear nylon reinforced tubing from
Lowes or Home Depot the same size as your raw water intake tube. Get
a double hose barb to go into this and and join with your raw water
intake tube.

4. Close your raw water seacock.

5. Fill the bucket with fresh water and dump in a whole bunch of red
food coloring.. take the line off your raw water inlet and connect it
to the tubing.

6. Prime the system by pouring the red water into the clear tubing
and then hold your thumb over the end while you lower the end back
into the bucket of water.

7. Start the engine and using your thumb see if there is suction at
the end of the tube in the water. You can easily see if there are
bubbles or if the water is backflowing because you have used red
water.

8. Assuming you have suction indicating the raw water pump works,
disconnect the raw water pump outlet and observe the flow there.

9. Flow beyond the raw water pump only means the blockage is after
this point.

I forget how the raw water flows but it was not obvious to me without
the manual. I also forget exactly where I found the blockage but I
vaguely remember it was either where the water enters the heat
exchanger or the mixing elbow, cant remember. I do remember I had to
be looking toward the starboard side to see the blockage. Since my
engine access is from port side, I had to use a mirror. I used a
penknife, ice pick and internal battery terminal wire brush cleaner to
clear the blockage. No amount of solvent would have done the job.
Try to remove the chips.

I also vaguely remember being sorta aware of not getting water to
backflow so it enters the cylinder via the mixing elbow, not sure it
was really a concern.

10. After you find the blockage, rune several buckets of fresh water
throught he system before reconnecting the raw water.

11. When reconnecting the raw water, make sure you dont lose the
prime and make sure you have raw water flow.

BTW, you can also remove the innards of the heat exchanger and clean
them with stiff wire or replace them thus improving cooling.

GET THE MANUAL