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ctlow 06-09-2011 03:37 AM

Yanmar YM coolant leak
I'm starting season 3 with a Yanmar 3YM20, and it leaks coolant. There's always a little under the engine, but a tiny top-up twice a season has seemed plenty.

I changed the coolant the other day, as recommended/required, and as I was removing the pressure/filler-cap on the heat exchanger, loosening hoses/bolts, the leak intensified, and then became a very steady drip for a minute. It was just behind the crankshaft pulley, right on the front of the engine, very localized. I could not find a trail of it dripping from higher up somewhere, and at that point I had just detached the "fresh-water" hose on the front of the engine to do an initial drain.

So, that's weird. The system leaked when I de-pressurized it.

Since re-filling, I ran it for a while and then had to top it up a bit again - normal, I believe - but haven't actually seen any leaking.

Still, this worries me. I have a year to go on the warranty, I think, so am going to look it over one more time and call the installing mechanic, which is a nuisance (5-hour boat-trip away, although of course only 40 minutes by land, and he does do "marina-calls" ...).

I come across various Yanmar coolant leak pages on a web search, but nothing so far definitive that tells me what to do other than call for professional help.

Anyone familiar with this scenario?

Oh, and ... a vane broke a year ago on the impeller, so of course I replaced it and the new one has been fine. I took advice including from the mechanic and it was that it's all okay, but now he says it's not okay and I have to find the vane - which I will do (or he will if I can't). Connection with the coolant leak? They're different sides of the cooling system.

Thank you.


SVCarolena 06-09-2011 08:53 AM

It is doubtful both problems are connected. My guess is that the vane is in the heat exchanger. just remove the end cap where the raw water side enters. If you don't find it there, then it has to be in the hose between the exhanger and raw water pump. You should fix it, as eventually it could lead to a restriction and overheating.

If the leak is near the front of the engine, it may be the seals on the circulation pump. There should be a weep hole on the bottom behind the pully. Older Yanmar's had problems with plastic fittings for the block drain locations, but I'm guessing yours is new enough to have metal fittings. that said, you may want to make sure those drain petcocks are all closed snugly, just becareful not to overtighten.

Faster 06-09-2011 10:06 AM


So, that's weird. The system leaked when I de-pressurized it.
Maybe not so weird... you likely broke a cool-down induced vacuum condition when you opened things up.

ctlow 06-11-2011 06:30 AM

Thank you both. Will have to review with mechanic. Getting underneath my engine would be more than difficult (although I hear they have these things called "mirrors" for places like that ...)

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