GBM wrote:

"Don W" wrote


Several knowledgeable people have mentioned that marine engines exposed
to salt water corrode from the inside out, and it makes sense. Right
now, the engine seems to be in fine shape, but my nagging worry is about
how thin the iron around the water passages may be. Since it is cooled
by salt water, it seems that they are probably not only thin already,
but getting thinner--thin being a relative term of course. My thought
on adding FWC would be to run a 75%/25% mixture of antifreeze and fresh
water which would stop the block from getting any thinner.



Don,

At one time almost all engines were seawater cooled - Those older Yanmars
were much heavier than the later GM series and likely had much thicker wall
thicknesses. They are also equipped with anodes to reduce corrosion - Not
sure how many owners actually change these though - When we bought our boat,
I changed the anodes - they were partly used up, but still serviceable.
Might be worth checking to see if yours were replaced during rebuild. In the
early 80's, there was a drive to get lighter engines for sailboat use, and
the GM series provided that. And, most of the larger GM engines were
equipped with closed circuit cooling.

Our own boat has a 1978 Yanmar 2QM15 direct cooled. It spent most of it's
life in salt water - Never been overhauled and still runs perfectly.

Hey, that's my exact motor. Maybe we should form a club!


--
Stephen

-------

For any proposition there is always some sufficiently narrow
interpretation of its terms, such that it turns out true, and
some sufficiently wide interpretation such that it turns out
false...concept stretching will refute *any* statement, and will
leave no true statement whatsoever.
-- Imre Lakatos

If it ain't broke don't fix it!
Make sure there is a new anode on the engine and then run it until it
fails - or until you trade the boat off for a new one (which is far
more likely scenario)....

denny

"Denny" wrote in message
oups.com...
If it ain't broke don't fix it!
Make sure there is a new anode on the engine and then run it until it
fails - or until you trade the boat off for a new one (which is far
more likely scenario)....

denny


Change BOTH anodes. Our engine 2-cyl has one in front where water enters
block and one at rear on cylinder head. The front one is easy to get at -
located on a splitter pipe where water from pump enters block. Rear one not
so easy to get at - located on cylinder head!

Not sure about the 3-cyl diesel, but our 2-cyl has a front plate on head
that serves as the alternator support and another plate at the back that has
the second anode and the temperature sensor. These plates can be removed and
this exposes the inside flow cavity of the head. Our engine had some scale
and rust build up just inside these plates - I scraped it away, but the
metal below looked pretty solid. If the engine has been rebuilt, one would
think that these plates would have been removed - It may be worth having a
look (at least at the front one) and seeing if the passages are clean
inside.

GBM

I've ordered a Yanmar service manual for the
engine. When it arrives, I'll start checking
anodes, etc. One thing I know for sure needs
changing is the fuel filter setup.

Don W.

GBM wrote:

"Denny" wrote in message
oups.com...

If it ain't broke don't fix it!
Make sure there is a new anode on the engine and then run it until it
fails - or until you trade the boat off for a new one (which is far
more likely scenario)....

denny



Change BOTH anodes. Our engine 2-cyl has one in front where water enters
block and one at rear on cylinder head. The front one is easy to get at -
located on a splitter pipe where water from pump enters block. Rear one not
so easy to get at - located on cylinder head!

Not sure about the 3-cyl diesel, but our 2-cyl has a front plate on head
that serves as the alternator support and another plate at the back that has
the second anode and the temperature sensor. These plates can be removed and
this exposes the inside flow cavity of the head. Our engine had some scale
and rust build up just inside these plates - I scraped it away, but the
metal below looked pretty solid. If the engine has been rebuilt, one would
think that these plates would have been removed - It may be worth having a
look (at least at the front one) and seeing if the passages are clean
inside.

GBM

I have the same engine in my 1983 C&C and it runs perfectly. Now I
have to admit mine is FW cooled but I really don't think internal
corrosion is likely to kill the engine. More like bearings and cam
wearing out.
If you compare the specs for the 3HM and the 3GM you will see the HM is
actually a heavier duty engine, greater displacement, horsepower, oil
capacity, etc. You are better off with a maybe rebuilt 3HM than with a
3GM that has definitely not been rebuilt. When sailing offshore you
are more likely to have your engine die from gunks stirred up in the
fuel tank than from anything going wrong with the engine.

Well, I'm just hoping that it doesn't fail when
I'm 30 miles offshore and there's no wind ;-)

Don W.

Denny wrote:
If it ain't broke don't fix it!
Make sure there is a new anode on the engine and then run it until it
fails - or until you trade the boat off for a new one (which is far
more likely scenario)....

denny

"Stephen Trapani"

Our own boat has a 1978 Yanmar 2QM15 direct cooled. It spent most of
it's
life in salt water - Never been overhauled and still runs perfectly.

Hey, that's my exact motor. Maybe we should form a club!



Stephen,
This group is about as close as we will get - It's a good place to discuss
these things. Then there is also the forum at
http://www.marinedieseldirect.com/ .

I have not looked too closely at converting to fresh water cooling, but I
think someone once said I would need a different exhaust mainfold to do
this. Looking at cooling circuit, I am not so sure. I will start a new
thread about this.

GBM