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cooling system flush? 04 raw water cooled yan 1GM10 coming from salt water.?


Jan 20, 2005
Nauticat 321 pilothouse 32 Erie PA
just got a 'project boat' w an old 04 yan single cylinder 1 gm 10-- raw water cooled. people are suggesting i 'flush the engine''s cooling system' to get the salt out or " the salt deposits will interfere w cooling " and 'won't be dissolved by running the engine in fresh water.' has anyone ever done this ? raw water cooled = no heat exchanger and no antifreeze reservoir .
one suggestion was to empty the cooling system , shut the intake kingston cock and let white vinegar sit in the cooling system for a day or 2.... Note the last time the engine ran, it showed no sign of overheat. so maybe i just shouldn't worry about it.

all thoughts and ideas welcome.
Jan 30, 2012
Nor'Sea 27 - "Kiwanda" Portland/Anacortes
If the motor does not overheat that means the the cooling system works and so (as you say) why do anything?

Also (apart from no overheat symptoms) if there is no saltwater history it is difficult to imagine why one would be concerned with salt deposits. Salt does not precipitate from salt water at the low temperatures on the direct cooled Yanmar motors - your thermostat keeps the temperature at 105F or so. So the problem - if it exists will be calcium not salt - same as a boiler and the fix is the same as a boiler too. (Vinegar would take weeks not days and you need to circulate any acidic solution.)

If an overheat occurred regularly there are other more likely culprits in direct cooled motors. Internal water jacket occlusion/restrictions are very rarely the cause of overheats in direct cooled cases --- more so in heat exchanger cases.

In short - no overheat - no reason for concern.

Last edited:
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Nov 22, 2011
Ericson 26-2 San Pedro, CA
I note that you are using that engine in fresh water. So really, you have nothing to worry about. I, on the other hand, run my 1GM in salt water, so I'll go ahead and make a few comments in case they might be helpful to others.

The engine will get a certain amount of salt crystals in it (i.e., when running it in a salt water environment), as one can readily confirm by removing the zinc on the side of the engine to change it out and taking a peek. However, as mentioned, the thermostat on that engine is set to 108-deg. and this keeps the worst of it at bay.

I have set mine up with a valve so I can draw fresh water in from a bucket. I flush it out when I get back to the dock. I will add some SaltAway or possibly just dish soap to the water.

The techs at Depco Pump also recommend flushing it with fresh water because it's better for the pump seals and the impeller, especially when you let the engine sit for a while. The pump on the 1GM/1GM10 is not very robust as far as the seals go and develop leaks with little provocation. So running a fresh water rinse through it will extend their life and put off a pump rebuild/seal replacement.

I've included a picture of my setup.

E26--Fresh Water Flush 1.JPG