Engine water intake

[mregan]

Does the engine water intake need to be primed?  When adding antifreeze last fall the engine didn't want to suck in the antifreeze I was pouring in the top of the intake strainer. Posted about it here and someone mentioned the impeller might have broken.
At the boat today. Looked at the impeller, intact. Pulled the intake strainer. Clear. Hose from thru hull to strainer is clean.  Hose from strainer to water pump is clear. Hose from water pump to heat x clear.  Put everything back together. Tutned engibe on. No water coming out of the back of the boat. Pulled water pump apart. Had my daughter start the engine water pump is Turning so that is working. 
Seems like water isn't getting pulled into engine.
Took the hose from the water pump to the heat x off, at the heat x and  turned engine on. Wanted to see if I was getting water up to that point. Figured m aybe issue was after that point. No water came out after running for a minute or two.

[Ron Hill]

mre : The pump doesn't need to be "primed". 

I believe that your pump is just not pumping. Check your pump (beside the impeller) and make sure that the inside face of the cover is smooth and that you are using a paper thin gasket!  On my Oberdoffer or Sherwood, I've taken the pump faces (cover)and taken them to a machine shop and had them refaced.  Take some wet/dry wet 200 grit sand paper on a flat wooden block and sand the inside face of the cover untill it is flat with no wear groves.  That insures that the impeller is tightly seated inside the pump body and gets the best suction for the intake!!

A thought

[Jon W]

Remember to use the paper gasket or the o-ring not both at the same time.

[mregan]

I'll take another look tomorrow.  The inside face seems smooth looking at it today but I'll check again.  The odd thing is I replaced the impeller last July, it ran fine July-Sept, or it appeared to be running fine.  Just noticed the issue getting ready for winter.  Maybe I'll try another impeller tomorrow and see if that makes a difference.

[Stu Jackson]

I'll take another look tomorrow.  The inside face seems smooth looking at it today but I'll check again.  The odd thing is I replaced the impeller last July, it ran fine July-Sept, or it appeared to be running fine.  Just noticed the issue getting ready for winter.  Maybe I'll try another impeller tomorrow and see if that makes a difference.

Faceplate  Faceplate  Faceplate 

That's what I'd do first.  Just get some fine sandpaper and a small block of wood and rub it for a minute or two.  Try this before swapping the impeller, 'cuz if it works, you haven't had to do the impeller swap. 

One other question:  You said

Hose from strainer to water pump is clear.

How did you confirm this hose was "clear?"  When you took the hose off the pump, did water come out?  Did water come out of the top of the strainer when you took this end of the hose off?  Just troubleshooting for more info.

[mregan]

Took the strainer apart and checked it out. Then reconnected the strainer to the seacock  hose and opened the seasick. Water came out the barbed fitting where the hose to the water pump connects.

Strainer to water hose. Disconnected and blew through it with my mouth. Water sprayed out the other end.

So even a slight gap between the faceplate and impeller will cause the water to not flow?  I would think the impeller would have enough oomph to overcome that.

When I run the engine for a few minutes, then pull the faceplate off, the pump housing and hoses are dry like it hasn't pulled any water at all through. I would think if the faceplate gap was the issue it would pull something just maybe not enough.

[lazybone]

Suggest pulling the impeller out and examining it closely.  The vanes can develop cracks at the roots that are not easy to see while its in the case. 

[Stu Jackson]

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So even a slight gap between the faceplate and impeller will cause the water to not flow?  I would think the impeller would have enough oomph to overcome that.

When I run the engine for a few minutes, then pull the faceplate off, the pump housing and hoses are dry like it hasn't pulled any water at all through. I would think if the faceplate gap was the issue it would pull something just maybe not enough.

Yes, slight gap does that.  Impeller width is the issue, has nothing to do with oomph.  If the "seal" isn't there, it won't pump.  Forward end of impeller has to touch all of the inside of the faceplate.

No, any gap will do it.  Just get it flat, and see. 

If it's not that, and you've checked the impeller, come back and we'll all take it the next step.

[scgunner]

mregan,

There seems to have been a problem recently with a batch of impellers, the rubber impeller has been separating from the brass sleeve that fits on the pump shaft, so the shaft and sleeve spin but the impeller doesn't. It happened to me and a couple of others. I installed the new impeller at the end of last season did a run up, everything worked good. First start this season, no water pumping.

The first thing I'd do would be to crank the motor with the pump cover off to visually to confirm the impeller is spinning. If it is then you've got an air leak somewhere between the impeller and the seacock that's breaking the vacuum.

[mregan]

Went down this morning and tried Stu's technique with the sandpaper.  It worked! Put everything back together, turned the engine on and water started coming out of the exhaust.  Let it run for a while, temp got up to 160* and held.   Thanks for all the help everyone, appreciate it.

[waughoo]

Great news.  Glad you got it solved and thanks for letting us know what the resolution was.  I'm certain this will help someone else one day.

[mregan]

Yes, I'm sure it will.  Great wealth of knowledge on this forum.   It was a small amount of sanding I did with very fine sandpaper.  Amazing how the pump went from no flow to full flow with just that little amount of sanding.

[Ron Hill]

Mre : It has been written up a number of times before in both the Mainsheet tech notes and on this form about raw water pump maintenance!!

The impeller MUST be seated tightly inside the pump housing to gain suction.  The face plate will wear from the impeller rotation and must be resurfaced periodically to where it is smooth again. 
To resurface I recommend that you take # 200 wet dry paper and wet it.  Place the wet paper on flat piece of wood  (I staple the paper to hold it in place) Then take the face plate of the pump inside facing down and slowly "sand" the plate face in-circular motion until your fingernail tells you the face plate is smooth.  I then repeat that process with #400 wet/dry wet paper again!!
As I previously mentioned I have extra face plates and every few years I take them to a machine shop to have them resurfaced!!

During winter layup I take the impeller and squirt some silicon on the impeller and reverse it on the shaft so the blades get to bend in the opposite direction for the next year!!  That is - after I bend each blade back to make sure there is no cracking evident!!

If you have trouble getting the impeller on its shaft into the housing - I use some liquid soap so it will slide in easily and lube the turning impeller until the water does that job!!

A few thoughts

[Stu Jackson]

mr,

So very glad to hear of your success.

Ron beat me to it, but it was actually his idea(s) that I've had success with over the years.

Some of you may recall that my PO gifted me with 11 years of Mainsheet magazines when I bought Aquavite in 1998.  I read them all.  On Christmas Day 1998 I started what became the Tech Notes Index.  Eventually the wise skippers in the IA "funded" putting all of these online for IA members.

I was one of the many of us who "graduated" from replacing their raw water pumps because rebuilding it "was more expensive than replacing it" based on the local shop's advice, to working on them, and eventually rebuilding a few of my own.   Two years ago I had to replace a stud in the gear cover case to hold my pump on!  Yeah, it's Tech Note...

Funny, but IIRC Ron's done "How To Rebuild" both Sherwood and Oberdorfer Pump articles!

So, yeah, it's all there.

But the great part of this forum is that when a question comes up, we find out how to fix it and/or a link and explain how to do it.  Never tire of repeating good help.

Glad it worked for you.

Oh, BTW, how's your impeller? :D:D

[ewengstrom]

As an aside to this thread and hopefully to help others in the future.
When we were performing the initial "survey" of our C-34 one of the things that the PO stated was that the motor ran well.....but that he'd had to have the impeller replaced because the impeller had failed. He did have this work done the day before the survey but when we started the motor it was not pumping water. We focused on the raw water pump and I did find that the gasket was leaking so I replaced that and started the engine again....no water.
Making a long story short, after much head scratching and searching I found that the original type strainer located just above the seacock had a very slight crack in it along a seam. Air is MUCH easier to pull than water so it simply would not pull water into the raw water pump.
This is just another item to check along with the raw water pump itself. I'll bet they don't crack often but it can happen and should be considered if everything else appears to be working correctly.