Yanmar 3YM20 drain plug weeping

[Lucky Duck]

Over the last few weeks I have noticed that the drain plug just after the raw water pump has been 'weeping'. The amount leaking seems unrelated to actual engine hours.

Have just loosen and retightened the drain plug in case that was the issue. However that doesn't seem to have made any noticable difference.

Could it be symptom of something else?

The engine is just over 5 years old and has roughly 750 hours on the clock

 

[RichardS]

Is there a drain plug just after the raw water pump? I've never spotted one but when I remove the pump I disconnect the hoses and the water drains out that way.

Is it in the pump casting itself or somewhere in the actual hose which runs up to the heat exchanger? There is a drain at the opposite end of the heat exchanger but that's a long way from the pump.

Richard

 

[Lucky Duck]

Is there a drain plug just after the raw water pump? I've never spotted one but when I remove the pump I disconnect the hoses and the water drains out that way.

Is it in the pump casting itself or somewhere in the actual hose which runs up to the heat exchanger? There is a drain at the opposite end of the heat exchanger but that's a long way from the pump.

Richard

Its fitted about a third of the way along the hose running from the raw water pump to the engine.

The 'bung' is undone or tightened using a small Allen key

 

[RichardS]

Its fitted about a third of the way along the hose running from the raw water pump to the engine.

The 'bung' is undone or tightened using a small Allen key

That sounds like the bung in the freshwater circulating coolant system but you would identify that immediately from the antifreeze which should be in the drips.

The raw water pump simply pumps seawater through a much smaller diameter hose from the pump to the heat exchanger. If there is a seawater bung in that hose, I can honestly say that I have never noticed or used it, unless it's not present on the 3YM30.

If I recall correctly, the bung has a rubber O-ring on it so it sounds as if you need to replace the O-ring and use plenty of silicone grease on it when you replace it. Do not over-tighten it as that is likely to make the leak worse. The same probably applies to a bung in the seawater hose.

EDIT .... a bit of research says that you are right and there is the same bung in both hoses. As said, replace the O-ring and use plenty of silicone grease. I would never remove it again as it seems a a pointless complication. Just remove the hose from the pump although I'm not sure why you would want to drain it other than to remove the pump anyway.

Richard

 

[Lucky Duck]

That sounds like the bung in the freshwater circulating coolant system but you would identify that immediately from the antifreeze which should be in the drips.

The raw water pump simply pumps seawater through a much smaller diameter hose from the pump to the heat exchanger.

If you are talking about the circulating coolant system, there has to be antifreeze/anticorrosion in the drips coming out. If there is no colour in this dripping liquid, then you need to rectify this as a matter of urgency. It could be partly the reason why the bung is leaking as its seat might well have corroded.

Richard

The diagram in the top left of page 35 of the manual calls it the 'seawater drain plug' as opposed to the 'coolant drain plug' or the 'coolant drain cock' (top right diagram)

The seat is rubber which might have perished in some way?

My concern is that something could be causing a 'back pressure' although there is no obvious shortage of water coming out if the exhaust

Have checked the coolant level because, as you say, that would be much more serious

 

[RichardS]

The diagram in the top left of page 35 of the manual calls it the 'seawater drain plug' as opposed to the 'coolant drain plug' or the 'coolant drain cock' (top right diagram)

The seat is rubber which might have perished in some way?

My concern is that something could be causing a 'back pressure' although there is no obvious shortage of water coming out if the exhaust

Have checked the coolant level because, as you say, that would be much more serious

I edited my post above as you were typing.

There will be some back pressure from the water trap although that will be increased if the exhaust elbow or heat exchanger are clogged up. However, I doubt whether that is the problem. Is there an O-ring on the bung? If so, that is the solution.

If the bung does bear down directly onto the rubber of the hose, and that is damaged it would cause the drips. Firstly try with the silicone grease and, if that doesn't work, then put a film of cling film or piece of thin polythene bag over the bung and nip it up again.

Ultimately, you can always purchase a new Yanmar hose but you could probably just buy a length of generic coolant hose and forget about the bung. If you do get it to stop dripping with the bodges, the don't ever remove it again.

Richard

 

[[163233]]

Yeah, there's one in the sea water pipe on the 3YM30 as well. It might be worth taking the end cover off the heat exchanger where that pipe goes in and checking for debris. I found a few bits of old impeller in mine.

The bung appears to be pointless, so maybe just take the hose off, dry it all out, and sika the bung in permanently.
I think that a Yanmar original hose would be about 60 quid.