Raw water pump - maintenance and spares?

Now that my fresh-water circuit is back in business, thinking about the raw water pump.

I have an oberdorfer N202M-16. I have a spare impeller, but wondering...
-- what other spares should I have? O-ring? ___?
-- and, does it need maintenance? E.g., fill the grease cup periodically, or...?

also, I don't have a sea strainer between the thru-hull and the pump. Thinking I should add one, but open to input.

Thanks in advance,
Bruce

water pump

I added a sea strainer to my system this spring. After about 15 hours of motoring it is interesting to see what it picks up. But it does give me peace of mind especially in the fall when you have all those little leaves on top and below the water. I also have an Oberdorfer pump. I just changed the impeller and did not put the O ring back on. I have read many times on this web page that they are not really necessary as the face plate hold the impeller in place. Where is it going to go? So far I have about 6 hours on the engine this way and no issues yet. I did save the old O ring and have 2 more back up impellers "just in case".

...I think you mean the snap ring, not the O-ring. But... the way those pumps fail is that the impeller rubbing against the face plate wears down the metal, and water starts going around the impeller instead of exiting the pump. I revived one by lapping the cover plate on a piece of sandpaper until all the wear marks disappeared, but probably only a temporary reprieve. Meanwhile, I install the snap ring.

toddster said:

...I think you mean the snap ring, not the O-ring. But... the way those pumps fail is that the impeller rubbing against the face plate wears down the metal, and water starts going around the impeller instead of exiting the pump. I revived one by lapping the cover plate on a piece of sandpaper until all the wear marks disappeared, but probably only a temporary reprieve. Meanwhile, I install the snap ring.

Click to expand...

By "snap" you mean how fast the thing disappears into your boat when it flies off the shaft. Having taken my Oberdorfer apart four times this spring, I don't think the snap ring has any function beyond allowing you to put the impeller on the shaft while off the engine. The shaft itself (on mine) is notched on engine end, and floating freely in pump body and partially in the engine, and engages with a pin inside the engine. That means the whole shaft including impeller and snap-ring is free to slide in and out, and only the impeller being slightly press-fit into the pump body by the cover keeps that from happening, and also insures the cover is slowly worn down and scored alas. The cover-gasket is also a wear item that should be replaced. They are expensive at the marina !. So now I keep a spare gasket, and a spare impeller, a spare cover screw in case one drops below the engine, and a jar of vaseline, and I fill the little grease cup screw with marine lithium grease and give it a turn every so often to push grease into the shaft bearing area. The vaseline can be packed into the impeller housing to help prime, a trick I learned from the mechanic at the marina. Also might be needed when getting bill from marina :nerd:

WRT Strainer, make sure you mount it where you can easily drop it below waterline and open drain plug to make sure you get all the air out of it. I think an air pocket in the strainer was the cause of many of my failure-to-prime episodes now that I am getting more familiar with my boat.

debonAir said:

... now I keep a spare gasket, and a spare impeller, a spare cover screw in case one drops below the engine....

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where's a good place to buy parts for the oberdorfer? I checked West, Fisheries, Defender, didn't find much...

bgary said:

where's a good place to buy parts for the oberdorfer? I checked West, Fisheries, Defender, didn't find much...

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https://www.fisheriessupply.com/oberdorfer-pump-n202m-flange-mount-bronze-impeller-pump-spares

Thanks. I saw that item, but it is for an N202M-15, and I have an N202M-16.... and haven't called yet to see if there are meaningful differences.

Bruce

Did a lot of research on this over the winter:

Defender.com sells the "factory" impeller for $35, or the similar Globe 815 "Run-Dry" impeller for $21.00

Downwindmarine.com sells a repair kit that includes impeller, snap ring, o-ring, lip seal, and carbon bearing for $55.00. Some sites charge this much for the impeller alone. Site also has useful parts diagrams.

Pumpsandpartsonline.com has similar parts and kits for similar prices.

Pumpvendor.com has the most extensive menu of every part for the pumps, but their prices seem higher.

Several vendors show listings for both the 202M-15 and -16. The internal parts appear to be the same, but apparently the M16 has 1/2" inlet/outlet vs 3/8" for the M15.

My pump plate has the o-ring gasket. I took the original o-ring to a hardware store to see if I could find a match. No luck on the shelves, but I narrowed it down to the correct size range. It is a size "034" o-ring (2 1/8" ID x 2 1/4" OD x 1/16" thick). Amazon carried a 5 pack of Viton 0-34s for $2.01 back in February. That is what I have on my pump now.

About the snap ring? I came to the same conclusion as debonAir: The pump shaft has a sliding "spline" (this is why you have to be careful not to pull the shaft out with the impeller when pulling the impeller. Since the snap-ring and the shaft are free to slide in and out of the pump assembly (until you tighten the faceplate), it is the faceplate that is holding things in place regardless of whether the snap ring is attached or not. I'm guessing that's why most people aren't able to get the snap ring back on--to do so would require sliding the shaft forward slightly, which is hard to do once you have already pushed the impeller into place.

Weed

bgary said:

also, I don't have a sea strainer between the thru-hull and the pump. Thinking I should add one, but open to input.

Click to expand...

I used my boat for 5 years before I installed one, and found no evidence that one was ever installed. I did have a strainer on the through-hull attached on the outside, but nothing inside. This is what I found after 5 years when I inspected the heat exchanger last year. Have a little weed.



And here's what I added just before last year's trip (Groco).

bgary said:

N202M-15, N202M-16.... meaningful differences.

Click to expand...

I found the datasheet for the N202M line here: http://www.oberdorferpumps.com/pumps/rubber-impeller-pumps/n202m/

It includes a parts listing



...which seems to indicate that the -15 and -16 use exactly the same parts except for the body, and the 11691 repair kit applies to both.

So, ordered one from Fisheries. Thanks for the link, GrandpaSteve! And all the great sourcing info, Kenneth.

Bruce

aaaaand, now a sea strainer, too.

ignacio said:

And here's what I added just before last year's trip (Groco).

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I added a small (WSB-750) strainer yesterday. And replaced all the hoses and fittings between the thru-hull and the heat-exchanger. There seems to be more water flowing out the back, now, which should probably not be surprising considering how crudded-up the old hoses were.

Hardest parts of the job were finding all the various hose fittings I needed, and figuring out where the waterline-level was inside the boat.

I positioned the strainer above the waterline so that I could drop and clean the basket without flooding the boat (and, as a fail-safe to avoid sinking the boat if the strainer fails in some way - recommended by Don Casey).

bgary said:

I added a small (WSB-750) strainer yesterday.

Click to expand...

Well, crap. Did a little reading this morning, and... should have done it yesterday.

Turns out - despite the assurances of the West Marine staff that this was a sea-water strainer - according to Groco this is a *fresh* water strainer, not intended to be used with salt-water.

So... it's coming out today. And a Groco ARG-755 will be going in as soon as it arrives from Fisheries.

Bruce,

Funny, I bought the same strainer last year (the WSB 750 you show installed). I've seen many engine photos where this seems to be used as the raw-water strainer. I liked its compact size compared to the bronze Groco strainers. I'd be interested to hear from others who have used this as a raw water strainer.

Also, what hose size do you have from the seacock to the raw water pump? I originally had 5/8" hose which required some custom fittings. I recently had some work done on the boat and the guy changed the hoses out to 1/2 hoses with standard fittings. I've been wondering if 1/2" hose is too small (but, maybe it comes down to the Oberdorfer M15 vs M16--the M15 has 1/2" ports).

Kenneth K said:

Also, what hose size do you have from the seacock to the raw water pump?

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I had a hodge-podge of hoses.... 5/8" from seacock to Oberdorfer, and 5/8" spliced down to 1/2" from Oberdorfer to heat exchanger, ending in a 1/2" connector at the HX.

I replaced with 1/2" throughout, except for a stub at the sea-cock - I spliced in a 5/8"-to-1/2" adapter there.

Mainly for two reasons:
-- the existing installation had 1/2" supply going into the heat exchanger, and any bigger hose upstream of that wouldn't result in greater volume through the system, and
-- I couldn't find any 5/8NPT-to-5/8"-hose fittings anywhere local.

The ports on the Oberdorfer N202M-16 are actually 5/8NPT (the literature says the ports are .500-14 NPT but 1/2"-NPT fittings are too small) s

At some point (?) I'll probably order the necessary fittings and make the plumbing 5/8" end-to-end, but at this point... my theory is that it's getting at least as much water through as it did before, and it's now straining out any weeds/debris, so.. it moves lower on my priority list for right now.

Thanks. Great to know. My mechanic insisted that since it is a 1/2" port on the pump, having over-sized hoses does nothing. At least all my fittings are now ABYC compliant.

I'm still tempted to install that Nylon strainer. Are you sure it's incompatible with salt-water. Also, what made you decide on the ARG 750 vs ARG 500? I've been weighting all these same decisions myself.

I like the board you installed to mount the strainer. I've been trying to decide whether to do the same, or to build a whole wall on the starboard side of the engine compartment (similar, I think, to what they did on the 32-200). The wall might add a little more noise damping, and might provide future options for relocating the fuel pump and fuel filters for easier maintenance. Any thoughts?

Mariah's on the hard again. I had a leak below my galley sink seacock. PO installed a 1 1/2" Marelon ball valve atop the 1 1/4" Marelon thru-hull. The PVC bushing he used to make the two parts fit split lengthwise, giving me a steady leak below the ball valve.

It's always somethin.........

The same raw water strainer shown in the pic a few posts above was installed on our boat when I bought it 11 years ago. It has always worked well, has not changed it deteriorated in any way, and continues to do the job well. I don't see why it would only be for fresh water use as mentioned above - - even the metal screen inside has not corroded at all. Unless someone can convince me of a problem with it, it's staying put.
Frank

Kenneth K said:

I'm still tempted to install that Nylon strainer. Are you sure it's incompatible with salt-water.

Click to expand...

Heh. You know me... I'm not sure of *anything* when it comes to engine stuff.

But here's what Groco says about the WSB-750 on their webpage... (emphasis added)


...so, yeah, my inference is that the WSB isn't even "meant" to be an engine raw-water strainer. It's not even listed in the "raw water strainers" section on their products page. I was mildly nervous about not having a bronze-bodied unit anyway, so this info broke the tie.

Does it work? Yes. Will I worry about it being the wrong thing for the job? Yes.

So, I figure better safe than sorry. If I'm using it for engine raw-water, I can't entirely cross it off my list until I have installed one that Groco actually says is designed to be for engine raw-water.

Kenneth K said:

Also, what made you decide on the ARG 750 vs ARG 500?

Click to expand...

Mostly size and configuration. The ARG-500 and ARG-755 are both the same physical size (6-1/2" tall)...but the -500 has 1/2" ports and the -755 has 3/4" ports, so... future-proof if I decide to up-size the hoses. The ARG-750 is - according to the datasheet at https://www.groco.net/products/raw-water-strainers/basket-strainer/arg-series - 8-1/2" tall, and I think (?) that's bigger than I need for the volume I'm putting through.

$.02

Yikes on the thru-hull!!! We still gotta figure out a time and place to get the two sisters together before the season is over....

Now that I thought I was a raw water pump expert... it quit working. Boat sat at the mooring for over a week. Started the engine up and had raw water working fine, then on the way out put the main up, heeled a little bit and... no raw water. Restarted a few hours later, no raw water. The strainer is completely full, and about the same level as the pump, which is a few inches above waterline. I've replaced the gasket, and impeller, and tightened the clamps etc. so now I'm at a loss as to what to do. On launch this Spring, the mechanic packed the impeller with vaseline and that seems to do the trick. I did that myself a few weeks back and it worked again for me, but I can't just keep packing the pump each time I use the motor. Plus where's all that vaseline ending up? the exhaust mixer or HX?

Any thoughts on 1) do I buy a new oberdorfer or 2) buy a rebuilt kit type thing? 3) use a different type of pump?

It seems like the new oberdorfers have an o-ring and a male-key shaft. Mine has a paper gasket and a female-key shaft but (I think) there is a short little double-male adapter key shaft inside. Is the new pump's shaft long enough to replace the adapter key thingy?

Advice appreciated!

debonAir said:

Now that I thought I was a raw water pump expert... it quit working. Boat sat at the mooring for over a week. Started the engine up and had raw water working fine, then on the way out put the main up, heeled a little bit and... no raw water. Restarted a few hours later, no raw water. The strainer is completely full, and about the same level as the pump, which is a few inches above waterline. I've replaced the gasket, and impeller, and tightened the clamps etc. so now I'm at a loss as to what to do. On launch this Spring, the mechanic packed the impeller with vaseline and that seems to do the trick. I did that myself a few weeks back and it worked again for me, but I can't just keep packing the pump each time I use the motor. Plus where's all that vaseline ending up? the exhaust mixer or HX?

Any thoughts on 1) do I buy a new oberdorfer or 2) buy a rebuilt kit type thing? 3) use a different type of pump?

It seems like the new oberdorfers have an o-ring and a male-key shaft. Mine has a paper gasket and a female-key shaft but (I think) there is a short little double-male adapter key shaft inside. Is the new pump's shaft long enough to replace the adapter key thingy?

Advice appreciated!

Click to expand...

Have you done any checking beyond the pump? Your symptoms and actions seem to indicate the pump is working with "perfect" conditions inside with the Vaseline coating, but maybe it has to work harder because there is a partial blockage in the inlet hose or thru-hull, or the outlet hose, the heat exchanger or the hose or fitting that connects to the exhaust elbow. Depending on the age and construction of your hoses, they can degrade and potentially block flow when under suction or pressure. A large air bubble at the top of the strainer will also interrupt water flow.

Its hard to tell how much back-pressure is normal in the system as the boat is new to me.

The thru-hull goes to the strainer, (groco, clean) and then to the pump with 5/8 hard walled hose. The strainer is mounted at about the same height as the pump. If I take the output line off the pump, there is NO water coming out when it isn't working. If I do the vaseline trick, the water comes out the pump fine, I reconnected the output hose, and the system works fine for hours after that. To me that indicates the problem is the pump itself. I will try pushing water backwards through the HX I think, how to get water pressure on the mooring will be my next adventure.

Not sure what causes it to stop working. It didn't work at launch time. It didn't work after sailing on a slight heel to port (5-10deg) twice now, but that could be coincidence. The boat was on the hard for 3 years or so before I bought her. The HX is the newer 3 inch replacement and I put a new zinc in (5424 came with a 2 inch HX originally)

Even new, the pump doesn't have a high flow rate right? Mounted a few inches above waterline it shouldn't be pulling too hard, and the manual says the pump can lift 15 feet!! of water. I've tried a few new impellers, rubber and the Globe run-dry (which don't seem to work as well)

Looking into a new pump, I think I need a N202M-07, as mine has the female-slot shaft. It *seems* like I could get the -15 model though, with the male key shaft, and remove the 4 to 2 hole adapter plate? Does that make sense to anyone? Seems the -15 has a grease-cup-free carbon shaft bearing which is nice.