Raw Water Pump Woes

[bratzcpa]

good evening!

I'm broke down at Indiantown, Florida. Fortunately, I've got a spot on a dock - all is safe!

Catalina 320, 2001 Yanmar 3GM30 engine. Johnson F4B-903 water pump.

It's NOT pumping water. I'm generally pretty good at troubleshooting, but I'm stuck. Here's what I've tried doing/checking so far:

1. raw water thru hull is open!
2. raw water strainer is clear.
3. when I remove the raw water hose from the pump, it freely flows from the static pressure outside the hull (so I know the pump is getting plenty of water flow to it).
4. when I pull off the hose from the heat exchanger (just downstream of the pump), there is virtually no flow (just a trickle, if that)- with the engine running. in the past when I've been working on things, I get a strong hose-like stream here.
5. I pulled the pump off and apart.
6. Nearly new impeller. All the vanes are in good shape. this is the new style impeller that as a screw straight through the center/core, so I'm pretty sure it's not a spun hub.
7. the "plate" on the pump is a little worn/scored, but I've seen a lot worse still working great.
8. Nearly new o-ring on the plate seal.
9. I'm seeing no leaks at all when the pump is sitting still, or when running.
10. I am missing 1 of the 6 screws that hold the plate on. It's been working fine like that for years - no problem.

I am about ready to just replace the whole blankety blank pump with a new one, but a) they're expensive, and b) I will lose 4 days waiting for the part to arrive.

Any thoughts? Anything else I can try? I would really really like to solve this problem and push off.

thx, markb

[MarkSF]

Check the hoses. I have heard of cases like yours where the hose has internally collapsed. Most likely on the intake hose, but could be the hose from pump to heat exchanger.

[colemj]

Is the cam missing? Plugged heat exchanger? If an impeller blade was lost in the past, it could be blocking or plugging the heat exchanger. Also, did you replace the zinc before this? Sometimes they are too long and block the flow of water through the heat exchanger (this depends on the placement of the zinc - I have no knowledge of your specific engine).

You can still have a spun hub with the center screw impeller.

Seems to me, the simplest experiment (after checking the above) is to slap in a new impeller and see what happens.

Mark

[model 10]

Run it without the cover on.

[keepondancin]

I had a pump once that acted the same way. Cover looked good, with some wear. After replacing the cover, it pumped as new. If the screw is missing because of being stripped, you can use a helio coil.

[colemj]

Originally Posted by Guy

Run it without the cover on.

????

I'm quite positive it won't pump water without the cover.

Mark

[model 10]

Originally Posted by colemj

????

I'm quite positive it won't pump water without the cover.

Mark

No ****, you could see if it's turning.

[RaymondR]

Can't help on your extant problem but I ran into the same cost issues myself and refused to pay the inflated cost of the Yanmar specific Johnston pump (which I was told is designed to a Yanmar spec re the mounting but in all other respects is a standard Johnston pump) and solved the problem by buying the standard Johnston, foot mounted, model and making a mounting bracket out of alloy angle.

[Wotname]

Originally Posted by bratzcpa

good evening!

I'm broke down at Indiantown, Florida. Fortunately, I've got a spot on a dock - all is safe!

Catalina 320, 2001 Yanmar 3GM30 engine. Johnson F4B-903 water pump.

It's NOT pumping water.................

7. the "plate" on the pump is a little worn/scored, but I've seen a lot worse still working great.
8. Nearly new o-ring on the plate seal.
..................

Any thoughts? Anything else I can try? I would really really like to solve this problem and push off.

thx, markb

You have covered almost everything already but I reckon the problem will be points 7 or 8.

You must remember the impeller must seal on three surfaces; the vane tips (obvious) and each side of the impeller (ie against the pump body and the cover plate). Any gap between the sides of the impeller and the body or cover seriously limit pump performance. You can get away with some wear but not much!

Your nearly new O ring might not be compressing enough especially with one screw missing or perhaps the wear / scoring has increased by a small margin.

In a pinch, I would try lightly facing the cover with some very fine wet & dry paper using a good flat surface (port glass???) and re-assembling without the O ring, just using some thin non hardening gasket sealant. Dunno what's in your area but Permatex make a few types

Or reversing the cover (suitably cleaned), again using a fine smear of sealant.

If that works, try refitting the O ring and check again.

Good luck

[jkishel]

"nearly new impeller" - I assume you mean that the impeller was recently replaced. It is possible that the replacement impeller was not exactly the right profile. It may have worked for a while then quit. Suggest you replace the impeller with exactly the correct model number, profile number, etc. and give that a try. Also double check all connections, the cam and the cover plate and gasket.

[bratzcpa]

Thx everyone for your thoughts. after a cold beer and some dinner, I'm thinking the most likely candidate is the scored cover plate. tomorrow morning, I'm going to lightly sand, buff, burnish the "front side" of the cover. its the same bronze ir brass material all the way through. also plan to remove, lubricate, and reassemble the o-ring .

I will report back tomorrow.

Markb

[jimbunyard]

All of the above, plus a worn cam also can make a flexible vane impeller pump not positive displacement. The big 'but' is that a flooded inlet/volute (sic) flexible vane impeller pump (as in your case) will usually function as a centrifugal pump and pump water even if its' positive displacement function is impaired or nil. At any rate, once you've verified supply, to properly troubleshoot the system you should next move to the pump outlet (as noted above there could be a problem with the hose from the pump outlet to the H/E)...

[dochip]

I had the same engine in my previous boat and a similar raw water pumping problem. Check the hoses ... my issue turned out to be collapsed interior of hose. Also, in the event you need replacement parts Mattos Marine in Fort Myers, less than an hour by car, might have what you need in stock so you wouldn't have to wait. Their number is 239-332-2515. Uber might help if you have to go there, but in a pinch I might be able to pick up the parts there and drive them out to you.

[DotDun]

Yammer used 2 models of that pump depending on where the engine was manufactured. The EU manufactured engine used a pump without a changeable cam, others used a model with a changeable cam.

Look at page 125 of the Depco Marine Catalog. Both models are on the top right of that page. The last time I bought the whole pump, cam-less model, from Depco it was ~$225. The model with the cam is about twice that price.

FWIW, pumps do wear out. I seen these pumps measure 1/2mm larger inside and refuse to pump, hence it may be a crap shoot as to whether you'll get it pumping again.

Good Luck!

[boeing1]

just worked on one with the same problem, with the hose removed from the heat exchanger no water flow, found heat exchanger was clogged flushed with salt away fixed the problem,