No Water From Exhaust After Sailing

[tomgrigsby]

I'm having a weird little event on restarting the engine (Yanmar 3GMD) after sailing. I have to leave the engine at idle for a few moments, and slow down if sailing well, in order to get water to come out of the exhaust. Sometimes I have to shut the engine off and restart it a couple of times to get water flow, or shut down and take off all way, then restart.
Water always flows on startup at the dock. It is just after being out that I'm having this happen. There is an anti-siphon valve tied in around the mixing elbow.
I'm wondering if while sailing that the water flow past the intake draws air into the pump? Maybe I should close the sea cock each time I secure the engine? Anyone run into this before?
I bought a new impeller, thinking that it was about to fail, but I haven't put it in yet. Water flows great ... when it flows

 

[Benny]

Sounds like air may be getting into the system or that you may have some intermitent blockage in the cooling passages. Remove and check all hoses and clamps. Make sure there is no sea grass or foreign bits in the system. Inspect the impeller for wear and make sure is properly seated to the shaft. I would use an air compressor with a high volume tank and blow air down the intake sea cock to clean out any sea grasses or others that may have gotten in there. Good luck.

 

[tomgrigsby]

Benny
Thanks for the input. Sounds like a good plan.

Is it normal to have an anti-siphon valve tied in around the mixing elbow - do most boats have this?

 

[Paul F]

It is my understanding that an anti-siphon valve is used if the cooling system is below the water line. On the boat I have the manifold and exhaust pipe are above the water line and there is no anti-siphon valve. Maybe others on here have more information.

 

[unknowncitizen]

very unusual

The water pump is of course upstream of the engine which is upstream on the mixing elbow and the anti-siphon and it's a positive displacement flexible impeller pump. Besides a restriction or leak, anything downstream of the pump discharge isn't a problem. Since you get flow on most occasions, with none ending up in the bilge, I'd say your problem has got to be on the suction side, or some weird problem with the impeller that only happens when sailing, but I can't think of what could be different about how the impeller would function at the dock vs sailing.

Again, these pumps are positive displacement, my experience is they will suck the water out of a bucket a foot or more below the pump even starting with the engine, pump and hoses bone dry. They are self priming.

Water flow going past the sea suction while sailing I guess may cause the pressure in the suction to go more negative then when you start it up at the dock, but since you've proven that it eventually will get going, it's not hoplessly plugged.

I'd say it's got to be one or a combination of: some mild fouling, a leak at the suction that only opens when the suction plumbing gets sucked into negative pressure or a weak suction hose that collapses when the extra suction required to start the flow while underway is applied.

 

[tomgrigsby]

Re: very unusual

Thanks for the input. I think my manifold and exhaust are above the water line, but I don't think I'll remove the anti-siphon valve. That is one of those "don't tear down the fence until you know why it was built" things. I'll check for a partial clog and collapsing hoses too. Thanks again all.

 

[aboardduet]

Any correlation between being on one tack or the other when still sailing? Might have something to do with which side of the keel the pickup tube exits the hull....??? Pro'bly not.....

-- Dave

 

[nick8489]

I had this problem

I'm having a weird little event on restarting the engine (Yanmar 3GMD) after sailing. I have to leave the engine at idle for a few moments, and slow down if sailing well, in order to get water to come out of the exhaust. Sometimes I have to shut the engine off and restart it a couple of times to get water flow, or shut down and take off all way, then restart.

I had a similar problem a few years back on an RL34 where the seacock for the raw water was about 1.5 m forward of the water pump. What happened when sailing hard without the engine running was that the seacock entry was exposed to the air and the water in the line discharged. When the boat came upright again it had a metre or so of air in the horizontal pipe and when you started the engine it could not suck it out. Eventually I solved the problem by drilling a new hole through the hull right under the pump and fitting a new seacock. Never had a problem again.

 

[tomgrigsby]

Re: I had this problem

It does seem that I have something like that going on. The seacock is about 1m away on the port side under the sink. The last time it happened, I started the engine with the port rail nearly in the water and still had nothing coming out of the exhaust until I took off all way, restarted the engine and let it idle until water flows (about 10 seconds). The rail was down because I was caught in a thunderstorm with all canvas flying and I wanted the engine because I was being blown out of the channel, but that's another story.
I suspect a venturi effect is pulling the water out of the feed line to the pump and maybe even draining down the engine a bit. I need to check the seacock for restrictions and collapsing hoses though too. Thanks again for the ideas and input.

 

[tomgrigsby]

Re: I had this problem

Just an update. Went out today and closed the sea cock as soon as I shut down the engine. 2 hours later on startup all was fine. Looks like a way around the problem at least.

 

[cbader]

Tom,

I have a Hunter 30 1979. It had the same issue. I fought this for over three months. My final solution was a new water pump. It turns out my water pump was allowing air in the system while sailing with the sea cock open. When I closed the sea cock during sailing and then opened before starting the engine work well but a pain. A friend that is a rocket engineer (no kidding, designs rockets) took one look at my old water pump, blew on the input and said it is bad. He said rebuild it or buy new one. I bought new one. To rebuild it by someone was $20.00 cheaper than new one. I have no issue with water or over heating now.

Carl

 

[tomgrigsby]

Carl
Thanks for the input. I have a new impeller and gasket that hasn't been installed yet, so I might as well go ahead and clutch at that last straw, but from the sounds of things probably the shaft seals are shot. If replacing the impeller doesn't fix it, I'll know what the next step is. I really appreciate the help. I would have been going crazy after replacing the impeller and still having the problem. What a great site this is. The shared experiences help us help save what llittle hair we have left. Fair Wiinds!

 

[pebrown1]

I attended a class for yanmar owners. One item pointed out is to check the anti-sphion valve for salt build thus preventing proper operation.

 

[tomgrigsby]

Looks like I need to get into the manual. I didn't know there was an anti-siphon valve, but that sure makes sense. I need to find out where it should be located. Thanks for the tip!