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

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