Raw Water Pump failed or...? (and difficulty to repair if so?)

Newsgroups Archive Prior to 2025
1

Hello—in my first (so far very happy) season with a Nonsuch. I’m very new to diesels and engine repair generally. I’m trying to diagnose and repair a problem on my 1986 NS 30U, which has a Westerbeke W27A, well maintained by the previous owners.

Over the past couple of outings I’ve noticed that the amount water coming out of the exhaust was diminishing, and on longer motoring passages (30-90 mins), the only water coming out of the exhaust was in the form of steam. On the last of these trips, probably about 30 mins of pushing against the current at moderate speed) the temp gauge was just above 200, making me very nervous.

The last time I planned to go out, no water at all came out of the exhaust when I started the engine (it usually starts spitting right away). Cancelled the sail and started diagnosing.

So far I have checked the through-hull, strainer, hoses from through-hull to strainer, strainer to pump, pump to heat exchanger.

I have also replaced the impeller, though it appeared to be in very good condition (see below–I was a little puzzled by the fact the impeller housing wasn’t perfectly cylindrical and that the fins on the existing impeller weren’t all pointing the same way.)

Just before I was about to tackle the heat exchanger, I tried running the engine with the pump/impeller output hose disconnected to see whether any water was coming out. Nothing came out.

Is it safe to assume, then, that my water pump is shot? Could there be another explanation? Is there anything else I need to check?

If the pump is shot, is it something a moderately handy person can replace himself, or is this an expert-level repair? It looks hard to do largely because on my boat the pump/impeller location is nearly impossible to access—we were only able to replace the impeller using mirrors and cameras to see around angles, and had to do a lot of it by feel—even though we have an inspection port in the starboard aft locker to get to it.

Really just looking for any suggestions, advice, words of wisdom/warning/encouragement. It’s my mother’s 80th birthday next weekend, and all she wanted was to go out sailing with me so I’m desperate to get it fixed (or else let her know it’s not going to happen…)

Thank you very much in advance…sorry for the long post!

George Weld
“Lionheart”
1986 Nonsuch 30U #352

Rhinebeck, NY

(attached are pictures of the previous impeller, which looked in good shape but odd fin position to me, and a picture to make sure I’m tackling the right area if I go in to change the raw water pump)

(attachments)

old impeller.jpeg
old impeller.jpeg1280×960 251 KB

IMG_0981.jpeg
IMG_0981.jpeg1280×960 366 KB

2

First off. That Engin mount set up is for a w27. Not the w27A. The raw water pumps are different. Different inlet and outlet.
The model is important for some of the parts.

Jules Verne. U30. 428. 1988
Abacos Bahamas
Steve Foose. ( pittsfield mass)

3

Ah thank you, my mistake, glad you caught!

4

George: the way to diagnose raw water circulation problems is to first make sure the strainer is not clogged up. If not, disconnect the hose from the strainer to the pump and see if water runs out. It should as that part of the system is below the waterline. If not, close the seacock, disconnect the hose to the strainer and momentarily open the seacock. Water should shoot out. Water should exit the strainer without the engine running and feed the pump. All these 30Us with the W27s are different as is the access to the pump. Is there some reason you can’t access the pump from the starboard lazerette?? I’ve found that the easiest way to replace that impeller is to remove the pump which I can normally do in about 20 minutes. If you are not a retired mechanic like myself, it will take longer but mechanics learn early on that removing more pieces easily is faster then removing fewer parts in the long run. I start by removing the strainer and hoses which gives me much more access. The pump is stamped with the manufacturer’s name – Oberdorfer, Sherwood, Johnson, etc. Some photos of my boat are attached (the fitting with valve is for flushing the engine)

Some hints – Don’t wrestle with getting hoses off, cut them and replace. Eliminate any 90 deg angles as then will inevitably plug up at some point so make the hoses longer to eliminate them. Consider just replacing the pump or overhaul it while it’s out as there are kits available.
Good luck,

Joe Valinoti
S/V iL Gatto NS30U #221
Sea Harbour YC
Oriental, NC USA


[details="(attachments)"]

![NS30U Raw Water.JPG|2288x1712](upload://4QEYKYNlccNMqWJqPvw4K5841Wd.jpeg)
![NS30U FlushValve001.jpg|2288x1712](upload://k8axzpIgxtAbU0YZZlPsfGRUP5U.jpeg)
![NS30U Flushvalve002.jpg|2288x1712](upload://BzQfzV5JlVEIuxl5evtuzZ2ElS.jpeg)

[/details]
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Mr Valinoti describes the way to proceed. Still, I want to add some information.

It looks like your strainer is above the water level. That means that the pump has to suck raw water up through the strainer. If the strainer is leaky (the seal of the lid), it could be that the pump is sucking air instead of water. Air is a lot thinner than water, you know.

And then there is the pump itself. Impeller pumps have “wearables” installed in the “wet part” of the pump. By “wet part”, I mean the part where the impeller spins. There are also replaceable parts on the dry side of the pump like a bearing and a seal.

  • First wet wearable is the impeller, this one is obvious.
  • Second wearable is the LID or cover of the pump. It should be absolutely flat. If the route of the impeller has created a nice, original looking, imprint > it is worn. You can try to mount the cover inside out to get a new flat surface. This is only possible when there is no text printed on the cover.
  • Third wearable is a plate that is mounted inside the pump. It has the same function as the plate, but it is mounted on the other side of the impeller. To explain: the top and bottom of the impeller are supposed to seal the in and output of the pump so it can build pressure. If the pump cover, and/or the plate on the other side of the impeller, are worn, the impeller-room becomes too big, compromising the pressure that is supposed to build, over the cam.
  • Fourth wearable, the cam. This is the (removable) thickening that is supposed to deform the impeller blades. It looks like a speed bump.

All nice and well, but what to do? Here is what I would do:

  • If your seacock (foul!) and your strainer are not blocked…
  • If your strainer is above the water level…

Check if the seal of the lid is not leaky.

  • If above is ok but still no water comes out the pump…

Look closely at the cover of your pump, the inside is the business part, so you need to unscrew :slight_smile:

  • If it is not flat, it is worn. Order a new pump cover, backing plate and cam for your pump but don’t give up getting under way!

Mount the cover inside out (only if outside is flat, no text should be printed on the outside of lid, some older models can’t be flipped for that reason)

  • If even that doesn’t help…

Run a hose from your seacock directly to the inlet of the pump. The worn pump does not have to suck UP water through the strainer this way. A worn pump may not be able to suck away the thin air to get the water UP when the strainer has been opened. It is waaaay easier for any impeller pump to suck water than air.

Good luck
mark h
n36#25
netherlands, europe

6

You can flatten the cover plate by putting some 600 emery paper on a piece of glass and sanding it flat on the surface.