Raw Water Flow Reduced After Impeller Change

[anacapaisland42]

The one that fooled me was when re-assembling the pump I put a wafer thin gasket (there wasn't one before) and that killed the water circulation!!
Bill

Originally Posted by Howler

Hello, I just changed the impeller and gasket in the water pump">raw water pump on our Yanmar 3GM30F. Before the service the raw water flow was great in terms of volume and frequency. After the service, it decreased to a trickle with lower frequency. I read Charlie's post on raw water flow, but am posting separately because there's such a clear "before and after" leading to doubt there are blockages upstream or downstream of the pump area.

The impeller is new and has self-adjusting blades. The belt driving the pump is properly tensioned and turning at normal speed.

Any ideas what I might have done wrong during the change leading to this reduction in flow?

A friend suggested that the system is picking up air. Any suggestions on how to test that hypothesis?

For now I plan to repeat the steps taken to see if anything turns up but I'd appreciate any suggestions. Thanks!

[boatpoker]

Summary .........

Look around the impeller cover plate .... any leakage ? this would suck air.

As someone said, check that your woodruff key is fitted (unless it's a splined shaft)

As someone else said, ensure that the rubber vane assembly is securely bonded to the impeller bushing. If it's been sitting on the shelf along time, that bonding could fail.

Take the cover off, turn over the engine briefly and see that the impeller is turning as it should.

Disconnect the input hose from the water pump, water should freely flow out unless the pump is above the waterline. If this is the case, loosen the top from the strainer, let it fill with water, tighten down and try again.

Disconnect the output hose from the pump, briefly run the engine and see if water comes out that hose.

[Lepke]

Something in older engine manuals is the recommendation to coat the inside housing, shaft and end plate with a finger full of waterproof grease. The grease helps suction for the first use and keeps impeller ends from being worn away in dry startups.
I've been using this system since the 60s and normally change my impellers at 5 years. I can't remember ever having one come apart, but I am getting old.

[Mike Banks]

It sounds to me as though the vanes on the impellor were facing the wrong direction when you replaced the imopellor. This means they are probably irreparably damaged and you will need to replace it again--this time with the vanes trailing the direction of rotation.

[boatpoker]

Originally Posted by Mike Banks

It sounds to me as though the vanes on the impellor were facing the wrong direction when you replaced the imopellor. This means they are probably irreparably damaged and you will need to replace it again--this time with the vanes trailing the direction of rotation.

An impeller in good condition will just auto-correct.

[Sailmonkey]

Originally Posted by Mike Banks

It sounds to me as though the vanes on the impellor were facing the wrong direction when you replaced the imopellor. This means they are probably irreparably damaged and you will need to replace it again--this time with the vanes trailing the direction of rotation.

That doesn’t happen. The vanes can go either direction, and do when the engine “rocks” at shutdown.

[SeaSon]

You forgot to open the sea cock.

[Howler]

Thanks for the additional posts. The impeller is bi-directional (that blades adapt to the direction the pump is turned). The seacock was definitely reopened. I did replace the thin gasket after carefully scraping the old one off with a razor blade (it had become encrusted on the cover plate).

Will check for the many other hypotheses today and report back.

[Howler]

Well, I came back to the boat today and here’s the epilogue. The answer is raw water gremlins! Everything worked fine after sitting for a few days. I can’t explain it other than maybe the new gasket “seasoned in” and produced a tighter seal. I’m very grateful for all the posts and learned many useful things for future troubleshooting.

[Olddan1943]

Originally Posted by CarlF

I agree it sounds like air from the pump not priming correctly. I'd replace the gasket again if you have a spare. It only takes a tiny air leak to make a pump act like this - easily caused by a tiny flaw in a new gasket.

Did the impeller you took out have all of its rubber vanes? If not, one or more may have lodged in the heat exchanger which can reduce flow. If there were any vanes missing, you have to open up the end of the heat exchanger closest to the pump and fish them out. On some engines you can just take the hose off and use long tweezers.

Remove one end of thee hose from the hull valve and blow out the entire system. OR you can remove hoses around the system in stages. It may be a clog in the heat exchanger.
When you get back to the boat, see if there is any sign of SW leakage on the pump.

[Howler]

Well, I came back to the boat today and here’s the epilogue. The answer is raw water gremlins! Everything worked fine after sitting for a few days. I can’t explain it other than maybe the new gasket “seasoned in” and produced a tighter sea (see Bill's post above). I’m very grateful for all the posts and learned many useful things for future troubleshooting, which I'm sure will be needed because I don't believe in gremlins .

[Olddan1943]

Originally Posted by Howler

Well, I came back to the boat today and here’s the epilogue. The answer is raw water gremlins! Everything worked fine after sitting for a few days. I can’t explain it other than maybe the new gasket “seasoned in” and produced a tighter sea (see Bill's post above). I’m very grateful for all the posts and learned many useful things for future troubleshooting, which I'm sure will be needed because I don't believe in gremlins .

Had you torqued the bolts tight before you left? No signs of saltwater leakage?

Next time you remove the end of the pump, check it for flatness in many directions with a flat edge.

Watch the pump for signs of saltwater leakage. Most pumps you can turn the end plate over and it will work fine.

Some times the magic happens when we are not looking.

[jackheape]

Water coolant update. Finally found the problem. The heat exchanger had clogged up with scale, even though I had just had it cleaned and pressure tested at a radiator shop. This is after changing the thermostat, impeller, and all the hoses. We figured, well, the only thing e haven't checked is the heat exchanger so we pulled it off. And found this...





Pulled the heat exchanger out, had it cleaned, then descaled it again and also the engine. Here is a picture of my home made descaling circulation pump.





Put everything back together and burped the engine.Everything runs great!