Intermittent Engine Water Issue

[PourDecisions]

So I have an intermittent cooling water flow issue on Yanmar 3YM30.

Sometimes when I start the engine, water doesnt flow, what is in the muffler spits out and then nothing. I've let the engine run for a couple of minutes, bringing it up to 3000. Sometimes I hear the muffler fill and it works well. Other times I shut it down and check the impeller and basket without any findings then try again only to have it work Sometimes, it starts up with out issue. I have put it in gear and drove the boat around and back down without resolution. But then sometimes it works.
Length of time sitting does not seam to be a determining factor.
Any thoughts? It feels like it's getting air locked, or something plugging the intake... But that is just a guess.

[Vento Solare]

When was the last time you replaced the impeller on the raw water pump?
Also check hoses and clamps on suction to pump.

[PourDecisions]

Full service beginning of the season.
No evidence of leaks that I can see.

[Vento Solare]

I would still check the impeller. Mine had two missing vanes after 4 months of hard use, resulting in similar issues you see. Used the Yanmar replacement impeller kit with the o-ring and all is good.

[JohnGreifzu]

I've had same issue. Is the water pump belt moving? For me, the water pump belt was one size too big and never tight enough. Got the right size on there and issue was resolved.

[Dan Corcoran]

I suppose we are all hesitating to suggest one or more formally broken impeller vanes (blades) are causing an intermitten full blockage, got past the heat exchanger and accumulate somewhere, because the symptom would not be a full blockage. Here is an article, different boat, same engine about what to look for if you go down this road.

https://forums.sailboatowners.com/threa ... es.141719/

Should you have the skills to start taking it apart, may as well take the enter assembly off the engine, bring it home, and do a full cleaning of the heat exchanger.

[Vento Solare]

Rather than taking off the heat exchanger, you can save time by doing a reverse flush it using a solution such as Barnacle Buster. I made a flushing system using a 5 gallon bucket, a 12V diaphragm pump purchased at a consignment shop and some spare hose. Disconnect the heat exchanger input and output, then plumb in the temporary hose so the pump takes a suction of the solution on the bucket, discharges to the outlet of the heat exchanger, and the input of the heat exchanger dumps back into the bucket. The initial minute did most of the cleaning, but I let it run for 30 minutes. Afterwards I dumped the solution and flushed with fresh water.

This will not remove any impeller blades stuck in the end bell. That can still be removed without removing the heat exchanger from the engine.

[PourDecisions]

Took me a couple days to get back to the boat. The impeller is good. And I checked the rubber attachment to the hub and that's good of course during the time I set aside to diagnose it started right up. Even after I pulled the impeller out and started to dry. Good thought on the heat exchanger back flush I'll see if I can pull that off. Surprised they don't put a strainer ahead of that for that very reason.

[PourDecisions]

I'm embarrassed to report that I think it's was the belt slipping sometimes

[Dan Corcoran]

LOL. Thank you for sharing yea, the symptoms didn't match up to blockage, but slippage? What was the cause of "sometimes" slipping, was it when the battery was partially discharged?

[PourDecisions]

No it wasn't related to battery state. The alternator is on a serpentine. It could be ( have been ? ) ambient temperature and maybe there is a glazed spot on the belt. I haven't changed it yet, just made it tighter and it hasn't happened since.