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Old 17-10-2011, 07:34   #1
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Troubleshooting Poor Raw Water Flow

I have a 27' Starwind with a 13hp Phasor (Beta Marine Clone) 2 cylinder. I hadn't run the motor in a month or so, but the last time we were out, it was running and cooling fine.

When I fired her up Sunday morning, it was flowing water out the exhaust, but it didn't seem quite up to what I was used to seeing. It was maybe half the usual flow, but it was still cooling at idle without a problem.

Once we put the boat in gear and revved it up, I started getting mostly steam out of the exhaust, and our temperature started rising. If I ran down at 1500rpm, it would flow enough water to cool the boat back down, so we creeped back in to the dock.

The raw water system is set up like this: through-hull > strainer > pump > heat exchanger > vented loop > mixing elbow > out the exhaust.

First thing we did was check the strainer. There were some remnants of sea life in the basket, but not enough of anything that it would have stopped water flow.

I then pulled the hose off the pump and blew back through the strainer. I could blow through with no problem, so the through-hull was not restricted.

I pulled the cover off the raw water pump. The impeller, which is less than a year old, still looks new.

I pulled the mixing elbow. It has some carbon build-up inside it, but not enough that it should have restricted exhaust pressure or caused excessive heat pockets. I cleaned it out and put everything back together.

None of this helped. I'm still getting half water flow at idle, and flow goes down and steam increases as a throttle up.

The heat exchanger was too hot to drain and take apart, so I'm going to pull the tubes out of it next weekend to check them, but it's been less than a year since I serviced them.

What am I missing? Aside from a potentially clogged heat exchanger is there anything else I should check? Why does water flow decline with RPMs?
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Old 17-10-2011, 07:37   #2
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Re: Troubleshooting poor raw water flow

1. Open the raw water pump and check the impeller.
2. Open the water strainer and see if it is clogged.

For #3 I'll let some one else give suggestions.
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Old 17-10-2011, 07:51   #3
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Re: Troubleshooting poor raw water flow

Funny Story..

About a month or so ago, I was having a similar issue. The water flow was just not normal.
I tried all the things that you tried to no avail. The guy a few slips down from me came over and said..." DAWN" " put some DAWN in there". I didn't think it could hurt anything and I had run out of options; so I took the hose off after the strainer ( before the pump/impeller ) and poured some liquid dawn in the hose ( a fair amt.) , chasing it with some water. Re-connected the hose and fired up the engine....believe it or not...The water started flowing better than ever. Give it a shot.... (Don't mind the suds.).
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Old 17-10-2011, 07:55   #4
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Re: Troubleshooting poor raw water flow

If the impeller has a brass hub, it may be spinning inside the impeller assembly. See this quite a bit....esp in the spring.
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Old 17-10-2011, 07:57   #5
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Re: Troubleshooting poor raw water flow

Steam, as opposed to White Smoke*, is often caused by a lack of sea water flow through a water-injected exhaust system. It's very difficult to make an assessment of water flow with a visual check.

It appears that you’ve eliminated the prime points in the system that are subject to causing a restriction or poor flow.

The most common causes are a clogged sea water strainer, a dirty heat exchanger, or a clogged water injection fitting on the wet exhaust elbow.

Also, make sure your engine can turn its full-rated RPM. If not, and the engine is overloaded, this can cause overheating. A dirty propeller or hull can cause this.

Don't rule out the thermostat. Even though the thermostat is in the fresh water cooling circuit (on fresh water cooled engines), it's possible the thermostat is sticking and not opening all the way. This restricts fresh water flow and will cause overheating.

* Steady white smoke; warm engine; any air temperature is bad news. The engine's coolant may be leaking into the combustion chamber, and creating a steady flow of steam. This is often caused by a leaking head gasket, or a crack in a cylinder head, most commonly in the exhaust port area. Usually requires serious surgery on the engine.

Good luck!
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Old 17-10-2011, 07:58   #6
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Re: Troubleshooting poor raw water flow

Being able to blow through thge thru hull from above does not mean it is fully clear. Is it a gate valve, Ball valve or real seacock?

Close it and take the hose off. get a bottle brush ready. Open it and quickly push the brush through a few times. A few gallons of water will not sink you. I found an eel in mine once!

If that does not work check the impelle to be sure the rubber has not separated from the hub. This happens more than you think. Usually due to sitting around dry and sticking to the pump housing. Pull the impelloer and make sure.
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Old 17-10-2011, 07:58   #7
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Re: Troubleshooting poor raw water flow

change the impellor even if it looks good
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Old 17-10-2011, 08:36   #8
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Re: Troubleshooting poor raw water flow

Back when I use to have a diesel engine on board I had a strange overheating problem. After changing the impeller (which was a real PITA BTW). It turned out there was a barnacle growing inside the intake hose. Check you intake hose if all else fails.
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Old 17-10-2011, 11:58   #9
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Re: Troubleshooting Poor Raw Water Flow

Atoll , good point. If you open it to look.... you might as well.
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Old 17-10-2011, 16:43   #10
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Re: Troubleshooting Poor Raw Water Flow

Had a similar issue some years ago, turned out to be the suction hose was not stiff enough and would collapse under increased suction.
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