Raw water pump - maintenance and spares?

That's the symptoms my old pumps have shown for case wear. Even mounted slightly below the waterline, barely any water went through them. I was able to revive one (temporarily?) by lapping the cover on sandpaper to remove all wear marks. Oh, also accidentally getting two paper gaskets instead of one in there produced the same symptoms, so I wouldn't use any kind of dressing compound on it.

Regarding pumping efficiency

Probably less useful advice for another part of the continent, but... in our boating area, the Columbia River eats raw water pumps. Well, not very fast, but the consumption part is true. In our case, the river carries in suspension very very fine sharp silt from glacier melt hundreds of miles upstream.
Over time, like maybe a thousand engine hours (to invoke a 'round' number) the pump chamber interior wears enough (i.e. enlarges) to lower pumping suction and efficiency.
My mechanic advised us to replace the original Oberdorfer when it sometimes hesitated to pull water after a rebuild. I had earlier lapped the slightly grooved face of the cover plate to get a better fit. I do like the O ring on the later model, also.

Anecdotal evidence that may not help you decide what to do, but call it another data point.

Regards,
Loren

Ok, you filled in a few blanks, so I can see why you suspect the pump. I have an old M7 with the 3/8" inlet-outlet.

These pumps are not going to gush, but they do move water well. It is hard for me to imagine that the pump body would wear out, but I suppose it's possible. These pumps are so simple, mechanically, that the things to check inside of it are few.

All the impeller vanes should be bent a little and the impeller vanes should be bent quite a bit more more on the outlet side. If that is true, then if the impeller is wide enough to rub the pump body and the cover, it's probably not the impeller size that is causing the problem. Are the surfaces inside the pump body and the cover all smooth?

Based on the vaseline trick it sounds like a wear problem or wrong size impeller.

Edit: And, based on toddster's and Loren's responses, I'm going to consider replacing my pump with the spare and see if my creeping engine temps are due to deficient raw water flow.

Thanks for all the input.

Since it is such a simple system, and it is a wear item, and I have no idea how long it has been in service, I am going to replace the pump and hope that that's the problem. If not then at least I know and am starting with a good pump.

I have the N202M-07 installed, but there does seem to be an adapter plate to go from 4 studs/nuts to 2 bolts, and the parts guy says the N202M-15 is compatible with my engine (5424 which is same as M30). I ended up ordering both, as he said I could return the one I don't use, and time I get on the boat is too short as it is. I'll try to -15 first if the nuts move, else I'll try the bolts and use the -07. The 15 has a carbon shaft bearing so no grease cup to futz with.

Speaking of parts guy: Scott at this place was good, and the price was 1/2 that I've seen in other places (almost cheaper than a used one on craigslist!!!) https://www.pumpsandpartsonline.com.../rubber-impeller/rubberimpellerpumps/N202M-07

Epilogue number 37....

I installed the new-new sea-strainer last night. Pulled out the Groco WSB-750 and installed a Groco ARG-755. Wow, in comparison, this thing is a *tank* compared to the WSB - bronze housing, tempered-glass bowl, significantly bigger.

Then I went out and ran the boat pretty hard for about a half-hour... 2700 rpm, 6.4 knots back and forth in front of the marina. The people on the balcony at Everett Yacht Club probably thought I was a kook (if only they knew...)

Everything ran great. Plenty of water coming out thru the exhaust, no leaks, I think it's time to button this up and head to Ludlow.

The only curious (?) thing I noted was that the engine never quite got up to the temp that was "normal" before all this started... normally this thing would run around 165-170F, yesterday, it never got over 150F. I...uh... didn't believe it, so I borrowed a dockmate's Fluke infra-red temperature gadget and, sure enough, temp at the manifold and at the thermostat housing was 146F.

Not sure if this is because the new hoses have less crud in them, or if the new fresh-water pump is doing a better job than the one that failed, or... something.

I'll keep an eye on it, because, well, I worry about changes I don't understand....

(edited to add a picture of the shiny new strainer...)

Epilog 38

I put a new pump in. I used the -07 model instead of the -15 model for two reasons

1) The bolts of the existing -07 came off easy, and the gasket under it was in OK shape, but stuck to the adapter plate I'd have to remove to install the -15.

2) Moyer Marine makes a bolt-on -07 replacement pump that has sealed ball bearings and probably will work better and longer than the OEM oberdorfers with the grease zerk or carbon shaft bearings. Wish I had seen this before I bought the OEM.

http://www.moyermarine.com/cgi-bin/...all&template=Templates/B000_storebuilder.html

Also replaced the two bolts and lock washers that were holding the old pump in place as they were rusted and washer cracked.

It seems to have fixed the issue. I primed the pump with half a tube of KY, and started the motor. The raw water is now about twice as much volume as I ever got with the old pump and I did a total of five engine runs, cold to fully hot, during and after various heel angles and it is still pumping happy.