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  #1  
Old 05-21-2013
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Slow water output at exhaust

Hello all
On a yanmar 3ym with 500 hours I have irregular output of water
Here are the symptoms I noted

When stalling , little stream of water, no smoke, then absolutely nothing for 10 seconds, then comes back , then some bursts of water, then another interruption, and then regular but low stream....and so on , like in a regular cycle.

At 1500 Rpm, lower than normal output, with 5 seconds interruption, than back but still lower than usual. White steam.

At 2500 Rpm lower than normal output, 5 seconds interruption, then normal output , followed by a longer interruption , lots of steam and then low output. At this point if I lower the Rpm I get better output and of course less steam.

The things I checked : intake seacock , water filter and water pump. Good output after the pump.

What would be your opinion ? Clogged heat exchanger ? Clogged mixing elbow?
Something else ?

Engine does not overheat ...yet...but need to fix the problem before it gets worse

Thanks for your help
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Old 05-21-2013
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Re: Slow water output at exhaust

Did you check the impeller on your raw water pump?
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Old 05-21-2013
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Re: Slow water output at exhaust

NEw ! And good strong steady output right after the water pump
Thanks
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Old 05-21-2013
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Re: Slow water output at exhaust

Water lift mufflers often behave as described.. once it 'fills' and the pressure evacuates it out the exhaust it can take several seconds before the waterlift fills enough again to offer enough restriction for the backpressure to 'push' it out again.

"Spurts" and trickles is not unusual UNLESS this is a new condition. Since your RWC pump seems to be doing the job I suspect you're OK... esp since there's no sign of overheating. However as I said if this is something new and markedly different from previous behaviour then it would be nice to know why it's changed...
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Re: Slow water output at exhaust

This happed to me on my 1GM, drove me crazy. I could pump water from a container all thru the engine at a good clip. I could run a rod down thru the water intake thru the seacock. What could it be?
Turned out was a bit of shell that had gotten just below the seacock and my rod would push it out of the way but when the impeller sucked it would lodge aqainst the ball valve and clog it.
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Re: Slow water output at exhaust

Could also be a matter of "losing prime" due to an air leak in a hose or fitting. Put a buicket full of water next to the hose for the intake and pump from it and watch your output, Be ready to refill said bucket several times. This became such a prob for me that I installed a priming elbow on my intake side with a ball valve opening to air allowing me to prime the system with water.
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Re: Slow water output at exhaust

You say it's a new impeller.. was the old one damaged? Could you have bits of the old one partially blocking your heat exchanger inlet?
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Re: Slow water output at exhaust

Thanks Faster but I changed the impeller as regular routine The old one was not damaged and can be used as a spare!
I just had my bottom cleaned by a diver so Frogwatch's idea of a clogged intake would make sense Except that I have a good strong and regular stream at the output of the water pump.
Still I will check my hoses for air intake Thanks
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Old 05-21-2013
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Re: Slow water output at exhaust

The water inlet on the exhaust elbow is sometimes susceptible to clogging, they are pretty small to start with and a little coking doesn't help.
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Old 05-21-2013
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Re: Slow water output at exhaust

Quote:
Originally Posted by capttb View Post
The water inlet on the exhaust elbow is sometimes susceptible to clogging, they are pretty small to start with and a little coking doesn't help.
That's the problem I had a couple of years ago with my 2gm20. The opening where the water gets injected into the exhaust was completely clogged with scale and carbon (there was also a lot of carbon buildup in the elbow). Replaced the mixing elbow and everything was fine. Try taking the hose off of the outlet side of the water pump and blowing into it. If there is anything more than the very slightest resistance the mixing elbow is likely to be the problem.
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